diff --git a/default.nix b/default.nix
index 8c24149..e219cbc 100644
--- a/default.nix
+++ b/default.nix
@@ -1,7 +1,6 @@
 {
   pkgs ? import <nixpkgs> { },
   lib ? pkgs.lib,
-  python ? pkgs.python3,
 }:
 
 let
@@ -16,7 +15,7 @@ let
   satisfiesSemver = (import ./semver.nix {inherit lib;}).satisfies;
 
   # Check Python version is compatible with package
-  isCompatible = pythonVersions: let
+  isCompatible = pythonVersion: pythonVersions: let
     operators = {
       "||" = cond1: cond2: cond1 || cond2;
       "," = cond1: cond2: cond1 && cond2;  # , means &&
@@ -27,7 +26,7 @@ let
     operator = if isOperator then (builtins.elemAt v 0) else acc.operator;
   in if isOperator then (acc // {inherit operator;}) else {
     inherit operator;
-    state = operators."${operator}" acc.state (satisfiesSemver python.version v);
+    state = operators."${operator}" acc.state (satisfiesSemver pythonVersion v);
   })
   {
     operator = ",";
@@ -47,12 +46,18 @@ let
   isBdist = f: builtins.match "^.*?whl$" f.file != null;
   isSdist = f: ! isBdist f;
 
+  mkEvalPep508 = import ./pep508.nix {
+    inherit lib;
+    stdenv = pkgs.stdenv;
+  };
+
   mkPoetryPackage = {
     src,
     pyproject ? src + "/pyproject.toml",
     poetrylock ? src + "/poetry.lock",
     overrides ? defaultPoetryOverrides,
     meta ? {},
+    python ? pkgs.python3,
     ...
   }@attrs: let
     pyProject = importTOML pyproject;
@@ -63,6 +68,8 @@ let
     specialAttrs = [ "pyproject" "poetrylock" "overrides" ];
     passedAttrs = builtins.removeAttrs attrs specialAttrs;
 
+    evalPep508 = mkEvalPep508 python;
+
     # Create an overriden version of pythonPackages
     #
     # We need to avoid mixing multiple versions of pythonPackages in the same
@@ -85,7 +92,10 @@ let
             then "wheel"
             else "setuptools";
 
-        in self.buildPythonPackage {
+          # Filter derivations by their PEP508 markers
+          markerFiltered = if builtins.hasAttr "marker" pkgMeta then (! evalPep508 pkgMeta.marker) else false;
+
+        in if markerFiltered then null else self.buildPythonPackage {
           pname = pkgMeta.name;
           version = pkgMeta.version;
 
@@ -101,7 +111,7 @@ let
           in builtins.map (dep: self."${dep}") dependencies;
 
           meta = {
-            broken = ! isCompatible pkgMeta.python-versions;
+            broken = ! isCompatible python.version pkgMeta.python-versions;
           };
 
           src =
@@ -126,7 +136,7 @@ let
           value = let
             drv = mkPoetryDep pkgMeta;
             override = getAttrDefault pkgMeta.name overrides (_: _: drv: drv);
-          in override self super drv;
+          in if drv != null then (override self super drv) else null;
         }) poetryLock.package;
 
       in {
@@ -134,13 +144,7 @@ let
         pytest_xdist = super.pytest_xdist.overrideAttrs(old: {
           doInstallCheck = false;
         });
-      } // builtins.listToAttrs lockPkgs // {
-        # Temporary hacks (Missing support for markers)
-        enum34 = null;
-        functools32 = null;
-        typing = null;
-        futures = null;
-      };
+      } // builtins.listToAttrs lockPkgs;
     in python.override { inherit packageOverrides; self = py; };
     pythonPackages = py.pkgs;
 
@@ -160,9 +164,9 @@ let
 
     # TODO: Only conditionally include poetry based on build-system
     # buildInputs = mkInput "buildInputs" ([ pythonPackages.poetry ]);
-    buildInputs = mkInput "buildInputs" ([ pythonPackages.setuptools ]);
+    buildInputs = mkInput "buildInputs" ([ pythonPackages.poetry ]);
 
-    propagatedBuildInputs = mkInput "propagatedBuildInputs" (getDeps "dependencies");
+    propagatedBuildInputs = mkInput "propagatedBuildInputs" (getDeps "dependencies") ++ ([ pythonPackages.setuptools ]);
     checkInputs = mkInput "checkInputs" (getDeps "dev-dependencies");
 
     passthru = {
diff --git a/pep508.nix b/pep508.nix
new file mode 100644
index 0000000..7c18e43
--- /dev/null
+++ b/pep508.nix
@@ -0,0 +1,185 @@
+{ lib, stdenv }: python:
+
+let
+
+  # Like builtins.substring but with stop being offset instead of length
+  substr = start: stop: s: builtins.substring start (stop - start) s;
+
+  # Strip leading/trailing whitespace from string
+  stripStr = s: lib.elemAt (builtins.split "^ *| *$" s) 2;
+
+  findSubExpressionsFun = acc: c: (
+    if c == "(" then (
+      let
+        posNew = acc.pos + 1;
+        isOpen = acc.openP == 0;
+        startPos = if isOpen then posNew else acc.startPos;
+        exprs = if isOpen then acc.exprs else acc.exprs ++ [ (substr acc.exprPos (acc.pos - 1) acc.expr) ];
+      in acc // {
+        inherit exprs startPos;
+        pos = posNew;
+        openP = acc.openP + 1;
+      }
+    ) else if c == ")" then (
+      let
+        openP = acc.openP - 1;
+        exprs = findSubExpressions (substr acc.startPos acc.pos acc.expr);
+      in acc // {
+        inherit openP;
+        pos = acc.pos + 1;
+        exprs = if openP == 0 then acc.exprs ++ [ exprs ] else acc.exprs;
+        exprPos = if openP == 0 then acc.pos + 1 else acc.exprPos;
+      }
+    ) else acc // {pos = acc.pos + 1;}
+  );
+
+  # Make a tree out of expression groups (parens)
+  findSubExpressions = expr: let
+    acc = builtins.foldl' findSubExpressionsFun {
+      exprs = [];
+      expr = expr;
+      pos = 0;
+      openP = 0;
+      exprPos = 0;
+      startPos = 0;
+    } (lib.stringToCharacters expr);
+  in acc.exprs ++ [ (substr acc.exprPos acc.pos expr) ];
+
+  parseExpressions = exprs: let
+    splitCond = (s: builtins.map
+    (x: if builtins.typeOf x == "list" then (builtins.elemAt x 0) else x)
+    (builtins.split " (and|or) " s));
+
+    mapfn = expr: (
+      if (builtins.match "^ ?$" expr != null) then null  # Filter empty
+      else if (builtins.elem expr [ "and" "or" ]) then {
+        type = "bool";
+        value = expr;
+      }
+      else {
+        type = "expr";
+        value = expr;
+      });
+
+      parsed = builtins.filter (x: x != null) (builtins.map mapfn (splitCond exprs));
+
+  in if builtins.typeOf exprs == "string" then parsed else builtins.map parseExpressions exprs;
+
+  # Transform individual expressions to structured expressions
+  # This function also performs variable substitution, replacing environment markers with their explicit values
+  transformExpressions = exprs: let
+    variables = {
+      os_name = "posix";  # TODO: Check other platforms
+      sys_platform = (
+        if stdenv.isLinux then "linux"
+        else if stdenv.isDarwin then "darwin"
+        else throw "Unsupported platform"
+      );
+      platform_machine = stdenv.platform.kernelArch;
+      platform_python_implementation = "CPython";  # Only CPython supported for now
+      platform_release = "";  # Field not reproducible
+      platform_system = (
+        if stdenv.isLinux then "Linux"
+        else if stdenv.isDarwin then "Darwin"
+        else throw "Unsupported platform"
+      );
+      platform_version = "";  # Field not reproducible
+      python_version = python.passthru.pythonVersion;
+      python_full_version = python.version;
+      implementation_name = "cpython";  # Only cpython supported for now
+      implementation_version = python.version;
+      extra = "";
+    };
+
+    substituteVar = value: if builtins.hasAttr value variables then (builtins.toJSON variables."${value}") else value;
+
+    processVar = value: builtins.foldl' (acc: v: v acc) value [
+      stripStr
+      substituteVar
+    ];
+
+  in if builtins.typeOf exprs == "set" then (
+    if exprs.type == "expr" then (let
+      mVal = ''[a-zA-Z0-9\'"_\. ]+'';
+      mOp = "in|[!=<>]+";
+      e = stripStr exprs.value;
+      m = builtins.map stripStr (builtins.match ''^(${mVal}) *(${mOp}) *(${mVal})$'' e);
+    in {
+      type = "expr";
+      value = {
+        op = builtins.elemAt m 1;
+        values = [
+          (processVar (builtins.elemAt m 0))
+          (processVar (builtins.elemAt m 2))
+        ];
+      };
+    }) else exprs
+  ) else builtins.map transformExpressions exprs;
+
+  # Recursively eval all expressions
+  evalExpressions = exprs: let
+    unmarshal = v: (
+      # TODO: Handle single quoted values
+      if v == "True" then true
+      else if v == "False" then false
+      else builtins.fromJSON v
+    );
+    hasElem = needle: haystack: builtins.elem needle (builtins.filter (x: builtins.typeOf x == "string") (builtins.split " " haystack));
+    # TODO: Implement all operators
+    op = {
+      "<=" = x: y: (unmarshal x) <= (unmarshal y);
+      "<" = x: y: (unmarshal x) < (unmarshal y);
+      "!=" = x: y: x != y;
+      "==" = x: y: x == y;
+      ">=" = x: y: (unmarshal x) >= (unmarshal y);
+      ">" = x: y: (unmarshal x) > (unmarshal y);
+      "~=" = null;
+      "===" = null;
+      "in" = x: y: let
+        values = builtins.filter (x: builtins.typeOf x == "string") (builtins.split " " (unmarshal y));
+      in builtins.elem (unmarshal x) values;
+    };
+  in if builtins.typeOf exprs == "set" then (
+    if exprs.type == "expr" then (let
+      expr = exprs;
+      result = (op."${expr.value.op}") (builtins.elemAt expr.value.values 0) (builtins.elemAt expr.value.values 1);
+      in {
+        type = "value";
+        value = result;
+      }) else exprs
+  ) else builtins.map evalExpressions exprs;
+
+  # Now that we have performed an eval all that's left to do is to concat the graph into a single bool
+  reduceExpressions = exprs: let
+    cond = {
+      "and" = x: y: x && y;
+      "or" = x: y: x || y;
+    };
+
+    reduceExpressionsFun = acc: v: (
+      if builtins.typeOf v == "set" then (
+        if v.type == "value" then (
+          acc // {
+            value = cond."${acc.cond}" acc.value v.value;
+          }
+        ) else if v.type == "bool" then (
+          acc // {
+            cond = v.value;
+          }
+        ) else throw "Unsupported type"
+      ) else if builtins.typeOf v == "list" then (
+        builtins.foldl' reduceExpressionsFun acc v
+      ) else throw "Unsupported type"
+    );
+  in (builtins.foldl' reduceExpressionsFun {
+    value = true;
+    cond = "and";
+  } exprs).value;
+
+in e: builtins.foldl' (acc: v: v acc) e [
+  findSubExpressions
+  parseExpressions
+  transformExpressions
+  evalExpressions
+  reduceExpressions
+]