diff --git a/src/manager.cpp b/src/manager.cpp
index ca462a2..13475d7 100644
--- a/src/manager.cpp
+++ b/src/manager.cpp
@@ -20,7 +20,7 @@ optional<Package> Manager::getPackage(string name) {
 
 bool Manager::install(std::string packageName) {
   // lookup package name (default to latest version)
-  auto pkg = package_list->lookup(packageName);
+  auto pkg = package_list->find_package(packageName);
 
   if (!pkg) {
     std::cerr << "Package " << packageName << " not found." << std::endl;
diff --git a/src/package.cpp b/src/package.cpp
index f0579e4..2b55335 100644
--- a/src/package.cpp
+++ b/src/package.cpp
@@ -119,13 +119,24 @@ void from_json(const json& j, PackageVersion& p) {
     j.at("files").get_to(p.files);
 }
 
+// find the latest compatible version
+// TODO expand filtering criteria beyond OS
 optional<PackageVersion> Package::latest_version(string os) {
-  optional<PackageVersion> latest;
+  optional<PackageVersion> latest_package;
+  optional<Version> latest_version;
+
+  for (PackageVersion pkg_ver : versions) {
+    if (pkg_ver.os != os) continue;
+
+    Version version = parseVersionString(pkg_ver.version);
+
+    if (version > latest_version) {
+      latest_package = pkg_ver;
+      latest_version = version;
+    }
 
-  for (PackageVersion ver : versions) {
-    if (ver.os != os) continue;
   }
-  return {};
+  return latest_package;
 }
 
 // converts a string of the format "1.2.3" into a Version struct
diff --git a/src/package_list.cpp b/src/package_list.cpp
index ecfa90b..d80e7c3 100644
--- a/src/package_list.cpp
+++ b/src/package_list.cpp
@@ -6,7 +6,9 @@ PackageList::PackageList() {
   // throw std::runtime_error("not implemented");
 }
 
-PackageList::PackageList(string filepath) {
+PackageList::PackageList(string filepath, string operating_system) {
+  os = operating_system;
+
   std::ifstream f(filepath);
 
   // TODO better error checks
@@ -27,20 +29,35 @@ PackageList::PackageList(string filepath) {
   }
 }
 
-optional<Package> PackageList::lookup(string name) {
-  // TODO get highest version (how do I do that?)
+optional<Package> PackageList::find_package(string name) {
   for (auto package: packages) {
     if (package.name == name) {
       return package;
     }
   }
+
   return {};
 }
 
-optional<Package> PackageList::lookup(string name, string version) {
+optional<PackageVersion> PackageList::find_latest_package_version(string name) {
+  // TODO get highest version (how do I do that?)
   for (auto package: packages) {
     if (package.name == name) {
-      return package;
+      string os = whichOS();
+      return package.latest_version(os);
+    }
+  }
+  return {};
+}
+
+optional<PackageVersion> PackageList::find_package_version(string name, string version) {
+  for (auto package: packages) {
+    if (package.name == name) {
+      for (auto package_version: package.versions) {
+        if (package_version.version == version) {
+          return package_version;
+        }
+      }
     }
   }
   return {};
diff --git a/src/package_list.h b/src/package_list.h
index 59a13bc..e9c8fc1 100644
--- a/src/package_list.h
+++ b/src/package_list.h
@@ -6,6 +6,7 @@
 #include <nlohmann/json.hpp>
 
 #include "package.h"
+#include "util.h"
 
 using json = nlohmann::json;
 using std::string;
@@ -17,14 +18,17 @@ using std::optional;
 class PackageList {
  public:
   PackageList();
-  PackageList(string filepath);
+  PackageList(string filepath) : PackageList(filepath, whichOS()) {};
+  // set OS explicitly for unit tests
+  PackageList(string filepath, string operating_system);
 
  public:
+  optional<Package> find_package(string name);
   // return latest (maybe latest && most compatible?) version of package
-  optional<Package> lookup(string name);
+  optional<PackageVersion> find_latest_package_version(string name);
 
   // return specific version of package
-  optional<Package> lookup(string name, string version);
+  optional<PackageVersion> find_package_version(string name, string version);
 
 
   /* static void from_json(const json& j, PackageList& pkg_list); */
@@ -32,6 +36,9 @@ class PackageList {
  private:
   // TODO could be a more efficient lookup implementation
   std::vector<Package> packages;
+
+  // set OS at initialization time
+  string os;
 };
 
 #endif
diff --git a/src/test/data/test-package-list.json b/src/test/data/test-package-list.json
index 83d60fe..c0808fa 100644
--- a/src/test/data/test-package-list.json
+++ b/src/test/data/test-package-list.json
@@ -10,11 +10,18 @@
             "keywords": ["KeywordA", "KeywordB"],
             "versions": [
                 {
-                    "version": "1.0",
+                    "version": "1.0.0",
                     "api_version": "9.0",
                     "language_version": "1.5.2.1",
                     "os": "linux",
                     "files": ["https://ccrma.stanford.edu/~nshaheed/chugins/Hydra/linux/butt.chug"]
+                },
+                {
+                    "version": "0.9.1",
+                    "api_version": "8.8",
+                    "language_version": "1.5.0.1",
+                    "os": "linux",
+                    "files": ["https://ccrma.stanford.edu/~nshaheed/chugins/Hydra/linux/butt.chug"]
                 }
             ]
         }
diff --git a/src/test/package_list_test.cpp b/src/test/package_list_test.cpp
index c6ff79d..b09e297 100644
--- a/src/test/package_list_test.cpp
+++ b/src/test/package_list_test.cpp
@@ -5,7 +5,7 @@ using std::optional;
 
 TEST_CASE("Load db file", "[PackageList]") {
   std::string path = "./data/test-package-list.json";
-  PackageList pkglist = PackageList(path);
+  PackageList pkglist = PackageList(path, "linux");
 
   Package want;
   PackageVersion version;
@@ -29,15 +29,50 @@ TEST_CASE("Load db file", "[PackageList]") {
 
   // Package want = {"John", "Butt", "1.0", "9.0", {{"linux", {"https://ccrma.stanford.edu/~nshaheed/chugins/Hydra/linux/butt.chug"}}}, "http://example.com", "http://repo.com", "specA", {"AuthorA", "AuthorB"}, "MIT", "DescriptionA", {"KeywordA", "KeywordB"}};
 
-  optional<Package> got = pkglist.lookup("Butt");
+  optional<Package> got = pkglist.find_package("Butt");
 
+  REQUIRE(got.has_value());
 
-  REQUIRE(got == want);
+  REQUIRE(got.value().name == want.name);
+  REQUIRE(got.value().versions.size() > 0);
+}
+
+TEST_CASE("Find Package") {
+  std::string path = "./data/test-package-list.json";
+  PackageList pkglist = PackageList(path, "linux");
+
+  SECTION("Successfully find package") {
+    optional<Package> pkg = pkglist.find_package("Butt");
+    REQUIRE(pkg.value().name == "Butt");
+  }
+
+  SECTION("Can't find package") {
+    optional<Package> pkg = pkglist.find_package("Fork");
+    REQUIRE_FALSE(pkg);
+  }
+}
+
+TEST_CASE("Find Package Version") {
+  std::string path = "./data/test-package-list.json";
+  PackageList pkglist = PackageList(path, "linux");
+
+  SECTION("Successfully find package") {
+    optional<PackageVersion> version = pkglist.find_latest_package_version("Butt");
+    REQUIRE(version.value().version == "1.0.0");
+  }
 
-  got = pkglist.lookup("Butt", "1.0");
-  REQUIRE(got == want);
+  SECTION("Can't find package") {
+    optional<PackageVersion> version = pkglist.find_latest_package_version("Fork");
+    REQUIRE_FALSE(version);
+  }
 
+  SECTION("Successfully find version") {
+    optional<PackageVersion> version = pkglist.find_package_version("Butt", "1.0.0");
+    REQUIRE(version.value().version == "1.0.0");
+  }
 
-  got = pkglist.lookup("NotReal");
-  REQUIRE_FALSE(got);
+  SECTION("Unsuccessfully find version") {
+    optional<PackageVersion> version = pkglist.find_package_version("Butt", "1.2.0");
+    REQUIRE_FALSE(version.has_value());
+  }
 }
diff --git a/src/uninstaller.cpp b/src/uninstaller.cpp
index e082cc2..8c6251c 100644
--- a/src/uninstaller.cpp
+++ b/src/uninstaller.cpp
@@ -7,7 +7,7 @@ Uninstaller::Uninstaller(PackageList* pkg_list) {
 
 bool Uninstaller::uninstall(std::string package_name) {
   // lookup package name (default to latest version)
-  auto pkg = package_list->lookup(package_name);
+  auto pkg = package_list->find_package(package_name);
 
   if (!pkg) {
     std::cerr << "BADBADBAD" << std::endl;