diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 2507587..e621c1e 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -8,17 +8,17 @@ repos:
   - id: trailing-whitespace
   - id: detect-private-key
 - repo: https://github.com/psf/black
-  rev: 22.12.0
+  rev: 23.3.0
   hooks:
     - id: black
       language_version: python3.9
 - repo: https://github.com/pycqa/isort
-  rev: 5.11.4
+  rev: 5.12.0
   hooks:
     - id: isort
       name: isort (python)
 - repo: https://github.com/charliermarsh/ruff-pre-commit
-  rev: v0.0.228
+  rev: v0.0.263
   hooks:
     - id: ruff
       args: ['--fix']
diff --git a/diadem/quantify/quant.py b/diadem/quantify/quant.py
new file mode 100644
index 0000000..d527543
--- /dev/null
+++ b/diadem/quantify/quant.py
@@ -0,0 +1,354 @@
+import math
+
+import numpy as np
+import polars as pl
+from loguru import logger
+
+
+def quant(ms_data: pl.DataFrame, pep: pl.DataFrame()) -> None:
+    """Main function.
+
+    Parameters
+    ----------
+    ms_data : pl.DataFrame
+        Mass spec data file.
+    pep : pl.DataFrame
+        Peptide data file.
+    """
+    # TODO: protein quant
+    # TODO: MAJOR OPTIMIZATION - I spent 2 days on this so there are LOTS
+    # of ways top optimize
+    # TODO: tests
+
+    # Match the peptide to spectra
+    pep_spectrum_df = match_peptide(ms_data, pep)
+    # Perform peptide quant
+    return peptide_quant(ms_data, pep_spectrum_df)
+
+
+def match_peptide(ms_data: pl.DataFrame, pep: pl.DataFrame) -> pl.DataFrame:
+    """Map the peptide to a peak in the mass spec data.
+
+    Parameters
+    ----------
+    ms_data : pl.DataFrame
+        Mass spec data file.
+    pep : pl.DataFrame
+        Peptide data file.
+
+    Returns
+    -------
+    pl.DataFrame:
+        DataFrame with the matched peptide and mass spec data.
+    """
+    # Initialize the dictionary that will be converted into the returned dataframe
+    data = {"peptide": [], "rt": [], "intensity": [], "mz": [], "ims": []}
+
+    # Iterate through each row of the mass spec data and find the corresponding peptides
+    # in the peptide dataframe.
+    for row in ms_data.rows(named=True):
+        # Convert the mzs to a series so they are easier to use
+        row["mzs"] = pl.Series(row["mzs"])
+        # Make sure we are looking at the correct precursor window
+        peptides = pep.filter(
+            (pl.col("PrecursorMZ") >= row["precursor_start"])
+            & (pl.col("PrecursorMZ") <= row["precursor_end"])
+        )
+        # Get all peptides at the given retention time
+        peptide = peptides.filter(pl.col("RetentionTime") == row["rts"])
+        # For each peptide at the retention time, find the most intense peak and sum
+        # across ion mobility
+        for p in peptide.rows(named=True):
+            # For each mz in the peptide mz list, get the mass spec mzs that are within
+            # .02 of that mz. This `grouped_mz` list contains lists of indicies of mzs
+            # from the mass spec data file that are close to the peptide mz.
+            grouped_mzs = []
+            for mz in p["mzs"]:
+                mzs = list(
+                    ((row["mzs"] <= mz + 0.02) & (row["mzs"] >= mz - 0.02)).arg_true()
+                )
+                # If those mzs have already been selected, continue. Otherwise add the
+                # values to a list.
+                if mzs in grouped_mzs:
+                    continue
+                else:
+                    found = False
+                    for group in grouped_mzs:
+                        if all(x in group for x in mzs):
+                            found = True
+                            break
+                    if not found:
+                        grouped_mzs.append(mzs)
+            # Initialize data to hold the information for the most intense peak
+            most_intense = 0
+            most_intense_mz = 0
+            most_intense_ims = 0
+            # Look at the mzs that are close to each other.
+            for group in grouped_mzs:
+                sum_intensity = 0
+                total_mz = 0
+                total_ims = 0
+                num = 0
+                # Sum mzs that are close to each other and average the mz and ims
+                for ind in group:
+                    if math.isclose(row["ims"][ind], p["IonMobility"], abs_tol=0.03):
+                        sum_intensity += row["intensities"][ind]
+                        total_mz += row["mzs"][ind]
+                        total_ims += row["ims"][ind]
+                        num += 1
+                    if sum_intensity > most_intense:
+                        most_intense = sum_intensity
+                        most_intense_ims = total_ims / num
+                        most_intense_mz = total_mz / num
+            # Add the most intense peaks to the data
+            data["peptide"].append(p["peptide"])
+            data["intensity"].append(most_intense)
+            data["rt"].append(row["rts"])
+            data["mz"].append(most_intense_mz)
+            data["ims"].append(most_intense_ims)
+
+    # Return the polars dataframe with the peptide-spectrum matched data
+    return pl.DataFrame(
+        data,
+        schema=[
+            ("peptide", pl.Utf8),
+            ("rt", pl.Float64),
+            ("intensity", pl.Float64),
+            ("mz", pl.Float64),
+            ("ims", pl.Float64),
+        ],
+    )
+
+
+def get_peaks(
+    ms_data: pl.DataFrame, row: dict, i: int, next_val: float, right: float = True
+) -> list:
+    """Helper function to get corresponding peaks of a peptide at different rts.
+
+    Parameters
+    ----------
+    ms_data : pl.DataFrame
+        Mass spec data file.
+    row : dict
+        Row of the peptide data that contains the peptide we are interested in.
+    i : int
+        Index of the peptide of interest in the mass spec data file.
+    next_val : float
+        Intensity of next peak either to the right or the left.
+        This help us to determine what part of the curve we are on (if we should stop
+        as soon as the intensities increase/level off, or if the values should increase
+        before they decrease).
+    right : float, default = True
+        True if we are looking at intensities to the right of the first measurement.
+        False if we are looking to the left.
+
+    Returns
+    -------
+    list:
+        List containing the intensities of the matching peaks at different retention
+        times. Another list of the retention times those peaks were found at.
+    """
+    # Initialize the lists that will contain the intensities/rts that we will return
+    intensities = []
+    rts = []
+
+    # Keep track of the previous intensity so you know if the intensities are
+    # decreasing or increasing. This could be simplified to just look at the
+    # last item in the intensities list, but I'll do that later.
+    last_val = row["intensity"]
+    # Keep track of the number of times the intensity isn't changing (i.e. peak is
+    # leveling off).
+    count = 0
+
+    # Here we determine if the peak is increasing or decreasing at this moment in time.
+    # If it is decreasing, we should stop once the intensities increase or level off.
+    # If it is increasing, we should see the intensities increase and then decrease.
+    break_if_up = True
+    if row["intensity"] < next_val:
+        break_if_up = False
+
+    # This is the loop that is getting all the intensities/rts for a peptide.
+    while True:
+        # If we are looking to the right of the matched intensity, make sure we are
+        # in the range of our data and go 1 rt to the right. Otherwise, go 1 rt to
+        # the left.
+        if right:
+            if i + 1 >= len(ms_data):
+                return intensities, rts
+            i += 1
+        else:
+            if i - 1 < 0:
+                return intensities, rts
+            i -= 1
+
+        # Get the intensity and rt of the peak
+        sum_intensity, rt = get_intensity_val(ms_data, row, i)
+
+        # Return the data if any of the following criteria is met:
+        #   1. the intensity is 0 of the current peak
+        #   2. the intensity is increasing when it should be decreasing
+        #   3. the intensity is leveling off
+        if (
+            sum_intensity == 0
+            or (break_if_up and sum_intensity > last_val + last_val / 1000)
+            or count >= 3
+        ):
+            return intensities, rts
+
+        # If the intensity is decreasing when it should be, append the information to
+        # our lists. Check if the values are roughly the same, meaning it is leveling
+        # off.
+        elif break_if_up and sum_intensity < last_val:
+            intensities.append(sum_intensity)
+            rts.append(rt)
+            last_val = sum_intensity
+            if sum_intensity > last_val + last_val / 1000:
+                count += 1
+            else:
+                count = 0
+
+        # If the intensity is increasing when it should be, append the information
+        # to our lists.
+        elif not break_if_up and sum_intensity > last_val:
+            intensities.append(sum_intensity)
+            rts.append(rt)
+            last_val = sum_intensity
+            count = 0
+
+        # If the intensity is decreasing when it should be increasing, this means
+        # we have gone over the top of our peak. Append the information to our
+        # lists and set `break_if_up` to True.
+        elif not break_if_up and sum_intensity < last_val:
+            break_if_up = True
+            intensities.append(sum_intensity)
+            rts.append(rt)
+            last_val = sum_intensity
+            count = 0
+
+        # If the intensities are the same, update the count and return if
+        # the count is 3 or more. Otherwise, append to intensities and rts.
+        elif last_val == sum_intensity:
+            count += 1
+            if count >= 3:
+                return intensities, rts
+            intensities.append(sum_intensity)
+            rts.append(rt)
+        else:
+            logger.info("Error: something weird happened")
+            return
+
+
+def get_intensity_val(ms_data: pl.DataFrame, row: dict, i: int) -> int:
+    """Helper function to get the intensity of a peak at a given retention time.
+
+    Parameters
+    ----------
+    ms_data : pl.DataFrame
+            Mass spec data file.
+    row : dict
+        Row of the peptide data that contains the peptide we are interested in.
+    i : int
+            Index of the peptide of interest in the mass spec data file.
+
+    Returns
+    -------
+    int:
+        Integer containing the intensity of the peak.
+        Integer containing the rt of the peak.
+    """
+    # Extract the relevant row from our mass spec data.
+    curr_row = ms_data[i]
+
+    # Get all mz values that are close to the peptide mz value.
+    s = list(
+        (
+            (curr_row["mzs"].item() <= row["mz"] + 0.02)
+            & (curr_row["mzs"].item() >= row["mz"] - 0.02)
+        ).arg_true()
+    )
+
+    # Sum the intensities to collapse the ims dimention.
+    sum_intensity = 0
+    total_mz = 0
+    num = 0
+    for ind in s:
+        if math.isclose(row["ims"], curr_row["ims"].item()[ind], abs_tol=0.03):
+            sum_intensity += curr_row["intensities"].item()[ind]
+            total_mz += curr_row["mzs"].item()[ind]
+            num += 1
+    return sum_intensity, curr_row["rts"].item()
+
+
+def peptide_quant(ms_data: pl.DataFrame, matched_df: pl.DataFrame) -> pl.DataFrame:
+    """Quantify peptides across rt.
+
+    Parameters
+    ----------
+    ms_data : pl.DataFrame
+        Mass spec data file.
+    matched_df : pl.DataFrame
+        Dataframe with peptide-spectrum matched data.
+
+    Returns
+    -------
+    pl.DataFrame:
+        DataFrame with the quantified peptides.
+    """
+    # Initialize the dictionary that will be converted into the returned dataframe
+    pep_quant_data = {"peptide": [], "intensity": [], "mz": [], "num_fragments": []}
+    # Add row numbers to the mass spec dataframe so I can easily go to the right
+    # and left rts (this can be changed later to something more elegant)
+    num_ms_data = ms_data.with_row_count()
+
+    # Iterate through each row in the peptide-spectrum matched dataframe and
+    # get the intensities for each peptide
+    for row in matched_df.rows(named=True):
+        # Get the row number in the mass spec dataframe for the current peptide
+        i = num_ms_data.filter(pl.col("rts") == row["rt"])["row_nr"].item()
+        # Get the intensities to the rt to the right and left of the current
+        # retention time. This can probably be moved to a different function
+        # or optimized later
+        sum_intensity_left, _ = get_intensity_val(ms_data, row, i - 1)
+        sum_intensity_right, _ = get_intensity_val(ms_data, row, i + 1)
+
+        # Get the intensities/rts that match the peptide in rts to the left of
+        # the current rt.
+        i_left, rt_left = get_peaks(num_ms_data, row, i, sum_intensity_left, False)
+        # These lists must be reversed since they will be added by going backward
+        # in rt.
+        if len(i_left) > 1:
+            i_left, rt_left = i_left[::-1], rt_left[::-1]
+        # Get the intensities/rts that match the peptide in rts to the right of
+        # the current rt.
+        i_right, rt_right = get_peaks(num_ms_data, row, i, sum_intensity_right, True)
+        # Get a list with all intensities/rts for the peptide
+        all_intensities = i_left + [row["intensity"]] + i_right
+        rt_left + [row["rt"]] + rt_right
+        # If there is more than one peak, do a trapezoidal integration
+        if len(all_intensities) > 1:
+            summed = np.trapz(
+                all_intensities
+            )  # tried to do `x=all_rts` but it gave me a weird answer
+        # If there are no peaks, something went wrong.
+        elif len(all_intensities) == 0:
+            logger.info("Error: no peaks were found")
+        # If there is only one peak, the intensity is the peak intensity
+        else:
+            summed = all_intensities[0]
+
+        # Store the data
+        pep_quant_data["peptide"].append(row["peptide"])
+        pep_quant_data["intensity"].append(summed)
+        pep_quant_data["mz"].append(row["mz"])
+        pep_quant_data["num_fragments"].append(len(all_intensities))
+
+    # Return the peptide quant dataframe
+    return pl.DataFrame(
+        pep_quant_data,
+        schema=[
+            ("peptide", pl.Utf8),
+            ("intensity", pl.Float64),
+            ("mz", pl.Float64),
+            ("num_fragments", pl.Float64),
+        ],
+    )
diff --git a/tests/conftest.py b/tests/conftest.py
index cd2bcec..716ad66 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,4 +1,5 @@
 import numpy as np
+import polars as pl
 import pytest
 from ms2ml import Peptide
 
@@ -168,3 +169,10 @@ def albumin_peptides():
 
     out = [Peptide.from_proforma_seq(f"{x}/2") for x in ALBUMIN_PEPTIDE_SEQS]
     return out
+
+
+@pytest.fixture
+def get_data(shared_datadir):
+    """Read the parquet files for the quant module and return the dataframes."""
+    return pl.read_parquet(shared_datadir / "small-ms_data.parquet"), \
+           pl.read_parquet(shared_datadir / "small-peptides.parquet")
diff --git a/tests/data/small-ms_data.parquet b/tests/data/small-ms_data.parquet
new file mode 100644
index 0000000..de7fa1f
Binary files /dev/null and b/tests/data/small-ms_data.parquet differ
diff --git a/tests/data/small-peptides.parquet b/tests/data/small-peptides.parquet
new file mode 100644
index 0000000..02b7962
Binary files /dev/null and b/tests/data/small-peptides.parquet differ
diff --git a/tests/quant_test.py b/tests/quant_test.py
new file mode 100644
index 0000000..524f160
--- /dev/null
+++ b/tests/quant_test.py
@@ -0,0 +1,75 @@
+import numpy as np
+import polars as pl
+from polars.testing import assert_frame_equal
+
+import diadem.quantify.quant as q
+
+
+def test_quant(get_data):
+    """Test that the entire module returns the correct data."""
+    ms_data, pep = get_data
+    quant_results = q.quant(ms_data, pep)
+    manual_results = pl.DataFrame(
+        {
+            "peptide": ["PEPTIDEEEE", "LESLIE", "EDITH"],
+            "intensity": [
+                np.trapz([610.00, 100.00]),
+                np.trapz([1111.00, (2210.00 + 1560.00), 4000.00]),
+                np.trapz(
+                    [
+                        110.8,
+                        110.8,
+                        110.8,
+                        123.1,
+                        456.4,
+                        765.7,
+                        321.3,
+                        110.8,
+                        110.8,
+                        110.8,
+                    ]
+                ),
+            ],
+            "mz": [100.01, np.average([249.99, 249.985]), 100.0],
+            "num_fragments": [2.0, 3.0, 10.0],
+        }
+    )
+    assert_frame_equal(manual_results, quant_results)
+
+
+def test_match_peptide(get_data):
+    """Test that the module correctly matches the peptides to the spectra."""
+    ms_data, peptides = get_data
+    match_result = q.match_peptide(ms_data, peptides)
+    manual_result = pl.DataFrame(
+        {
+            "peptide": ["PEPTIDEEEE", "LESLIE", "EDITH"],
+            "rt": [100.0, 150.0, 5.0],
+            "intensity": [610.00, (2210.00 + 1560.00), 123.1],
+            "mz": [100.01, np.average([249.99, 249.985]), 100.0],
+            "ims": [99.982, np.average([149.98, 150.01]), 100.0],
+        }
+    )
+    assert_frame_equal(match_result, manual_result)
+
+
+def test_get_peaks(get_data):
+    """Test that the quant module is accurately identifying the
+    corresponding peaks at different rts.
+    """
+    ms_data, peptides = get_data
+    pep_spectrum_df = q.match_peptide(ms_data, peptides)
+    row = pep_spectrum_df.row(
+        by_predicate=(pl.col("peptide") == "PEPTIDEEEE"), named=True
+    )
+    num_ms_data = ms_data.with_row_count()
+
+    r_intensities, r_rts = q.get_peaks(num_ms_data, row, 1, 100.0)
+    r_intensities_manual = [100.0]
+    r_rts_manual = [110.0]
+    assert r_intensities == r_intensities_manual and r_rts == r_rts_manual
+
+    l_intensities, l_rts = q.get_peaks(num_ms_data, row, 1, 0, False)
+    l_intensities_manual = []
+    l_rts_manual = []
+    assert l_intensities == l_intensities_manual and l_rts == l_rts_manual