diff --git a/MANIFEST.in b/MANIFEST.in
index 47706b0..e8e2cb1 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1,7 +1,7 @@
 include LICENSE
 include README.rst
-include requirements/base.txt
 
+recursive-include requirements *
 recursive-include tests *
 recursive-exclude * __pycache__
 recursive-exclude * *.py[co]
diff --git a/setup.py b/setup.py
index b8b1705..0df0a5f 100644
--- a/setup.py
+++ b/setup.py
@@ -27,7 +27,7 @@
     ],
     description=("Command line tool, that converts Common Cartridge " "courses to Open edX Studio imports."),
     entry_points={"console_scripts": ["cc2olx=cc2olx.main:main"]},
-    install_requires=load_requirements("requirements/base.txt"),
+    install_requires=load_requirements("requirements/base.in"),
     license="GNU Affero General Public License",
     long_description=readme,
     include_package_data=True,
diff --git a/utils.py b/utils.py
index 5f1f1e5..b1a9538 100644
--- a/utils.py
+++ b/utils.py
@@ -31,12 +31,74 @@ def load_requirements(*requirements_paths):
     """
     Load all requirements from the specified requirements files.
 
+    Requirements will include any constraints from files specified
+    with -c in the requirements files.
     Returns a list of requirement strings.
     """
-    requirements = set()
+    def check_name_consistent(package):
+        """
+        Raise exception if package is named different ways.
+
+        This ensures that packages are named consistently so we can match
+        constraints to packages. It also ensures that if we require a package
+        with extras we don't constrain it without mentioning the extras (since
+        that too would interfere with matching constraints.)
+        """
+        canonical = package.lower().replace("_", "-").split("[")[0]
+        seen_spelling = by_canonical_name.get(canonical)
+        if seen_spelling is None:
+            by_canonical_name[canonical] = package
+        elif seen_spelling != package:
+            raise Exception(
+                f'Encountered both "{seen_spelling}" and "{package}" in requirements '
+                "and constraints files; please use just one or the other."
+            )
+
+    def add_version_constraint_or_raise(current_line, current_requirements, add_if_not_present):
+        if regex_match := requirement_line_regex.match(current_line):
+            package = regex_match.group(1)
+            version_constraints = regex_match.group(2)
+            check_name_consistent(package)
+            existing_version_constraints = current_requirements.get(package, None)
+            # It's fine to add constraints to an unconstrained package,
+            # but raise an error if there are already constraints in place.
+            if existing_version_constraints and existing_version_constraints != version_constraints:
+                raise Exception(
+                    f"Multiple constraint definitions found for {package}:"
+                    f' "{existing_version_constraints}" and "{version_constraints}".'
+                    f"Combine constraints into one location with {package}"
+                    f"{existing_version_constraints},{version_constraints}."
+                )
+            if add_if_not_present or package in current_requirements:
+                current_requirements[package] = version_constraints
+
+    by_canonical_name = {}  # e.g. {"django": "Django", "confluent-kafka": "confluent_kafka[avro]"}
+    requirements = {}
+    constraint_files = set()
+
+    # groups "pkg<=x.y.z,..." into ("pkg", "<=x.y.z,...")
+    re_package_name_base_chars = r"a-zA-Z0-9\-_."  # chars allowed in base package name
+    # Two groups: name[maybe,extras], and optionally a constraint
+    requirement_line_regex = re.compile(
+        rf"([{re_package_name_base_chars}]+(?:\[[{re_package_name_base_chars},\s]+\])?)([<>=][^#\s]+)?"
+    )
+
+    # Read requirements from .in files and store the path to any
+    # constraint files that are pulled in.
     for path in requirements_paths:
-        requirements.update(
-            line.split("#")[0].strip() for line in open(path).readlines()
-            if is_requirement(line)
-        )
-    return list(requirements)
+        with open(path) as reqs:
+            for line in reqs:
+                if is_requirement(line):
+                    add_version_constraint_or_raise(line, requirements, True)
+                if line and line.startswith("-c") and not line.startswith("-c http"):
+                    constraint_files.add(os.path.dirname(path) + "/" + line.split("#")[0].replace("-c", "").strip())
+
+    # process constraint files: add constraints to existing requirements
+    for constraint_file in constraint_files:
+        with open(constraint_file) as reader:
+            for line in reader:
+                if is_requirement(line):
+                    add_version_constraint_or_raise(line, requirements, False)
+
+    # process back into list of pkg><=constraints strings
+    return [f'{pkg}{version or ""}' for (pkg, version) in sorted(requirements.items())]