diff --git a/MANIFEST.in b/MANIFEST.in
index d118234a..4072eba7 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -2,3 +2,4 @@ include requirements/base.in
 include requirements/test.in
 include LICENSE
 include README.rst
+include requirements/constraints.txt
diff --git a/setup.py b/setup.py
index db39c864..149d7e18 100644
--- a/setup.py
+++ b/setup.py
@@ -2,6 +2,7 @@
 
 
 import os
+import re
 import sys
 
 from setuptools import setup
@@ -16,35 +17,68 @@
 
 def is_requirement(line):
     """
-    Return True if the requirement line is a package requirement;
-    that is, it is not blank, a comment, or editable.
+    Return True if the requirement line is a package requirement.
+
+    Returns:
+        bool: True if the line is not blank, a comment,
+        a URL, or an included file
     """
-    # Remove whitespace at the start/end of the line
-    line = line.strip()
+    # UPDATED VIA SEMGREP - if you need to remove/modify this method remove this line and add a comment specifying why
 
-    # Skip blank lines, comments, and editable installs
-    return not (
-        line == '' or
-        line.startswith('-r') or
-        line.startswith('#') or
-        line.startswith('-e') or
-        line.startswith('git+') or
-        line.startswith('-c')
-    )
+    return line and line.strip() and not line.startswith(('-r', '#', '-e', 'git+', '-c'))
 
 
 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()
+    # UPDATED VIA SEMGREP - if you need to remove/modify this method remove this line and add a comment specifying why.
+
+    requirements = {}
+    constraint_files = set()
+
+    # groups "my-package-name<=x.y.z,..." into ("my-package-name", "<=x.y.z,...")
+    requirement_line_regex = re.compile(r"([a-zA-Z0-9-_.]+)([<>=][^#\s]+)?")
+
+    def add_version_constraint_or_raise(current_line, current_requirements, add_if_not_present):
+        regex_match = requirement_line_regex.match(current_line)
+        if regex_match:
+            package = regex_match.group(1)
+            version_constraints = regex_match.group(2)
+            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 BaseException(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
+
+    # process .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 and add any new constraints found 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
+    constrained_requirements = [f'{pkg}{version or ""}' for (pkg, version) in sorted(requirements.items())]
+    return constrained_requirements
 
 
 VERSION = '2.1.1'