diff --git a/Project.toml b/Project.toml
index 1ff84cd..4655c8e 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,9 +1,10 @@
 name = "PkgDeps"
 uuid = "839e9fc8-855b-5b3c-a3b7-2833d3dd1f59"
 license = "MIT"
-version = "0.1.0"
+version = "0.2.0"
 
 [deps]
+Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
 TOML = "fa267f1f-6049-4f14-aa54-33bafae1ed76"
 UUIDs = "cf7118a7-6976-5b1a-9a39-7adc72f591a4"
 
diff --git a/src/PkgDeps.jl b/src/PkgDeps.jl
index 1323369..81bb844 100644
--- a/src/PkgDeps.jl
+++ b/src/PkgDeps.jl
@@ -1,52 +1,42 @@
 module PkgDeps
 
+using Pkg.Types: VersionNumber, VersionRange
 using TOML: parsefile
 using UUIDs
 
 export PkgEntry, RegistryInstance
-export find_upstream_dependencies, reachable_registries
+export find_downstream_dependencies, reachable_registries
 
-struct PkgEntry
-    path::String
-    registry_path::String
-    name::String
-    uuid::UUID
-end
+include("pkg_entry.jl")
+include("registry_instance.jl")
 
-struct RegistryInstance
-    path::String
-    name::String
-    uuid::UUID
-    url::Union{String, Nothing}
-    repo::Union{String, Nothing}
-    description::Union{String, Nothing}
-    pkgs::Dict{AbstractString, PkgEntry}
-end
 
-function RegistryInstance(path::AbstractString)
-    d = parsefile(joinpath(path, "Registry.toml"))
-    pkgs = Dict{AbstractString, PkgEntry}()
-
-    for (uuid, info) in d["packages"]
-        uuid = UUID(uuid)
-        info
-        name = info["name"]
-        pkgpath = info["path"]
-        pkg = PkgEntry(pkgpath, path, name, uuid)
-        pkgs[name] = pkg
-    end
+"""
+    _get_latest_version(base_path::AbstractString)
+
+Get the latest VersionNumber for base_path/Versions.toml
 
-    return RegistryInstance(
-        path,
-        d["name"],
-        UUID(d["uuid"]),
-        get(d, "url", nothing),
-        get(d, "repo", nothing),
-        get(d, "description", nothing),
-        pkgs
-    )
+# Arguments
+- `base_path::AbstractString`: Base path to look for Versions.toml
+
+# Returns
+- `VersionNumber`: Highest version number found in base_path/Versions.toml
+
+# Throws
+- `VersionTOMLNotFound`: Versions.toml does not exist at the base_path
+"""
+function _get_latest_version(base_path::AbstractString)
+    versions_file_path = joinpath(base_path, "Versions.toml")
+
+    if isfile(versions_file_path)
+        versions_content = parsefile(versions_file_path)
+        versions = [VersionNumber(v) for v in collect(keys(versions_content))]
+
+        return first(findmax(versions))
+    end
 end
 
+
 """
     reachable_registries(registry_names::Array)
 
@@ -92,7 +82,7 @@ reachable_registries(registry_name::String; depots::Union{String, Vector{String}
 
 
 """
-    find_upstream_dependencies(pkg_name::AbstractString; registries::Array{PkgDeps.RegistryInstance}=reachable_registries())
+    find_downstream_dependencies(pkg_name::AbstractString; registries::Array{PkgDeps.RegistryInstance}=reachable_registries())
 
 Find all dependents of `pkg_name` for the current master version.
 
@@ -105,29 +95,38 @@ Find all dependents of `pkg_name` for the current master version.
 # Returns
 - `Array{String}`: List of packages which depend on `pkg_name`
 """
-function find_upstream_dependencies(pkg_name::AbstractString; registries::Array{RegistryInstance}=reachable_registries())
-    upstream_dependencies = String[]
+function find_downstream_dependencies(
+    pkg_name::AbstractString;
+    registries::Array{RegistryInstance}=reachable_registries()
+)
+    downstream_dependencies = String[]
 
     for rego in registries
         for (pkg, v) in rego.pkgs
-            path = joinpath(v.registry_path, v.path, "Deps.toml")
-
-            if isfile(path)
-                file_contents = parsefile(path)
-
-                dep_keys = [k for k in collect(keys(file_contents)) if endswith(k, "-0") || k == "0"]
-
-                deps = getindex.(Ref(file_contents), dep_keys)
-                deps = vcat(collect.(keys.(deps))...)
-
-                if pkg_name in deps
-                    push!(upstream_dependencies, pkg)
+            base_path = joinpath(v.registry_path, v.path)
+            deps_file_path = joinpath(base_path, "Deps.toml")
+
+            if isfile(deps_file_path)
+                deps_content = parsefile(deps_file_path)
+                dependency_versions = collect(keys(deps_content))
+                latest_version = _get_latest_version(base_path)
+
+                # Use the latest_version of pkg, and check to see if pkg_name is in its dependents
+                for version_range in dependency_versions
+                    if in(latest_version, VersionRange(version_range))
+                        dependencies = collect(keys(deps_content[version_range]))
+
+                        # Check if pkg_name is used in the latest version of pkg
+                        if pkg_name in dependencies
+                            push!(downstream_dependencies, pkg)
+                        end
+                    end
                 end
             end
         end
     end
 
-    return upstream_dependencies
+    return downstream_dependencies
 end
 
 end
diff --git a/src/pkg_entry.jl b/src/pkg_entry.jl
new file mode 100644
index 0000000..dd7c386
--- /dev/null
+++ b/src/pkg_entry.jl
@@ -0,0 +1,6 @@
+struct PkgEntry
+    path::String
+    registry_path::String
+    name::String
+    uuid::UUID
+end
diff --git a/src/registry_instance.jl b/src/registry_instance.jl
new file mode 100644
index 0000000..5ddd044
--- /dev/null
+++ b/src/registry_instance.jl
@@ -0,0 +1,33 @@
+struct RegistryInstance
+    path::String
+    name::String
+    uuid::UUID
+    url::Union{String, Nothing}
+    repo::Union{String, Nothing}
+    description::Union{String, Nothing}
+    pkgs::Dict{AbstractString, PkgEntry}
+end
+
+function RegistryInstance(path::AbstractString)
+    d = parsefile(joinpath(path, "Registry.toml"))
+    pkgs = Dict{AbstractString, PkgEntry}()
+
+    for (uuid, info) in d["packages"]
+        uuid = UUID(uuid)
+        info
+        name = info["name"]
+        pkgpath = info["path"]
+        pkg = PkgEntry(pkgpath, path, name, uuid)
+        pkgs[name] = pkg
+    end
+
+    return RegistryInstance(
+        path,
+        d["name"],
+        UUID(d["uuid"]),
+        get(d, "url", nothing),
+        get(d, "repo", nothing),
+        get(d, "description", nothing),
+        pkgs
+    )
+end
diff --git a/test/resources/registries/Foobar/Case1/Deps.toml b/test/resources/registries/Foobar/Case1/Deps.toml
index cef037f..4977338 100644
--- a/test/resources/registries/Foobar/Case1/Deps.toml
+++ b/test/resources/registries/Foobar/Case1/Deps.toml
@@ -1,2 +1,2 @@
 [0]
-UpDep = "000eeb74-f857-587a-a816-be5685e97e75"
+DownDep = "000eeb74-f857-587a-a816-be5685e97e75"
diff --git a/test/resources/registries/Foobar/Case1/Versions.toml b/test/resources/registries/Foobar/Case1/Versions.toml
new file mode 100644
index 0000000..61ed410
--- /dev/null
+++ b/test/resources/registries/Foobar/Case1/Versions.toml
@@ -0,0 +1,2 @@
+["0.0.1"]
+git-tree-sha1 = "7bbdd841302ae0708824fa57d77a3e4780097531"
diff --git a/test/resources/registries/Foobar/Case2/Deps.toml b/test/resources/registries/Foobar/Case2/Deps.toml
index ba36cd3..9548894 100644
--- a/test/resources/registries/Foobar/Case2/Deps.toml
+++ b/test/resources/registries/Foobar/Case2/Deps.toml
@@ -1,2 +1,2 @@
 ["0.1-0"]
-UpDep = "000eeb74-f857-587a-a816-be5685e97e75"
+DownDep = "000eeb74-f857-587a-a816-be5685e97e75"
diff --git a/test/resources/registries/Foobar/Case2/Versions.toml b/test/resources/registries/Foobar/Case2/Versions.toml
new file mode 100644
index 0000000..bd9349b
--- /dev/null
+++ b/test/resources/registries/Foobar/Case2/Versions.toml
@@ -0,0 +1,2 @@
+["0.1.0"]
+git-tree-sha1 = "7bbdd841302ae0708824fa57d77a3e4780097531"
diff --git a/test/resources/registries/General/Case3/Deps.toml b/test/resources/registries/General/Case3/Deps.toml
index f03f072..f3fe1c1 100644
--- a/test/resources/registries/General/Case3/Deps.toml
+++ b/test/resources/registries/General/Case3/Deps.toml
@@ -1,2 +1,2 @@
-["0"]
-UpDep = "000eeb74-f857-587a-a816-be5685e97e75"
+["1"]
+DownDep = "000eeb74-f857-587a-a816-be5685e97e75"
diff --git a/test/resources/registries/General/Case3/Versions.toml b/test/resources/registries/General/Case3/Versions.toml
new file mode 100644
index 0000000..d2f962b
--- /dev/null
+++ b/test/resources/registries/General/Case3/Versions.toml
@@ -0,0 +1,2 @@
+["1.1.1"]
+git-tree-sha1 = "7bbdd841302ae0708824fa57d77a3e4780097531"
diff --git a/test/resources/registries/General/Case4/Deps.toml b/test/resources/registries/General/Case4/Deps.toml
new file mode 100644
index 0000000..83c8b7e
--- /dev/null
+++ b/test/resources/registries/General/Case4/Deps.toml
@@ -0,0 +1,2 @@
+["0-0.1"]
+DownDep = "000eeb74-f857-587a-a816-be5685e97e75"
diff --git a/test/resources/registries/General/Case4/Versions.toml b/test/resources/registries/General/Case4/Versions.toml
new file mode 100644
index 0000000..36310db
--- /dev/null
+++ b/test/resources/registries/General/Case4/Versions.toml
@@ -0,0 +1,5 @@
+["0.1.0"]
+git-tree-sha1 = "7bbdd841302ae0708824fa57d77a3e4780097531"
+
+["0.2.0"]
+git-tree-sha1 = "36895c2e78b43dea83b9fdba6655886c107cdc98"
diff --git a/test/resources/registries/General/Registry.toml b/test/resources/registries/General/Registry.toml
index 24cb0af..ad67c1b 100644
--- a/test/resources/registries/General/Registry.toml
+++ b/test/resources/registries/General/Registry.toml
@@ -12,3 +12,4 @@ some amount of consideration when choosing package names.
 
 [packages]
 000eeb74-f857-587a-a816-be5685e97e75 = { name = "Case3", path = "Case3" }
+001eeb74-f857-587a-a816-be5685e97e75 = { name = "Case4", path = "Case4" }
diff --git a/test/resources/registries/README.md b/test/resources/registries/README.md
new file mode 100644
index 0000000..ed06824
--- /dev/null
+++ b/test/resources/registries/README.md
@@ -0,0 +1,19 @@
+## Creating test cases
+When adding test cases please create another test case in any existing registry.
+Include `Deps.toml` and `Versions.toml` files to specify when a package has been dependent
+on another.
+
+
+## Overview of Cases
+
+### Case1
+Single patch pre-1.0 release that has always been dependent on `DownDep`.
+
+### Case2
+Single minor pre-1.0 release that has always been dependent on `DownDep`.
+
+### Case3
+Single post-1.0 release that is dependent on `DownDep`.
+
+### Case4
+Two releases where `DownDep` was previously a depdenency and no longer is.
diff --git a/test/runtests.jl b/test/runtests.jl
index 8e458db..0e27845 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,7 +1,5 @@
 using PkgDeps
 using Test
-# Create some temp package TOML files
-# Test that we get them properly
 
 depot = joinpath(@__DIR__, "resources")
 
@@ -20,21 +18,22 @@ depot = joinpath(@__DIR__, "resources")
     end
 end
 
-@testset "find_upstream_dependencies" begin
-    @testset "specific registry" begin
-        foobar_registry = reachable_registries("Foobar"; depots=depot)
+@testset "find_downstream_dependencies" begin
+    foobar_registry = reachable_registries("Foobar"; depots=depot)
+    all_registries = reachable_registries(; depots=depot)
 
-        dependents = find_upstream_dependencies("UpDep"; registries=foobar_registry)
+    @testset "specific registry" begin
+        dependents = find_downstream_dependencies("DownDep"; registries=foobar_registry)
 
         @test length(dependents) == 2
         [@test case in dependents for case in ["Case1", "Case2"]]
     end
 
     @testset "all registries" begin
-        registries = reachable_registries(; depots=depot)
-        dependents = find_upstream_dependencies("UpDep"; registries=registries)
+        dependents = find_downstream_dependencies("DownDep"; registries=all_registries)
 
         @test length(dependents) == 3
+        @test !("Case4" in dependents)
         [@test case in dependents for case in ["Case1", "Case2", "Case3"]]
     end
 end