diff --git a/lib/vagrant/errors.rb b/lib/vagrant/errors.rb
index 8a66f436b..77296d8a9 100644
--- a/lib/vagrant/errors.rb
+++ b/lib/vagrant/errors.rb
@@ -316,6 +316,10 @@ module Vagrant
       error_key(:copy_private_key_failed)
     end
 
+    class CorruptMachineIndex < VagrantError
+      error_key(:corrupt_machine_index)
+    end
+
     class DarwinNFSMountFailed < VagrantError
       error_key(:darwin_nfs_mount_failed)
     end
diff --git a/lib/vagrant/machine_index.rb b/lib/vagrant/machine_index.rb
new file mode 100644
index 000000000..636318484
--- /dev/null
+++ b/lib/vagrant/machine_index.rb
@@ -0,0 +1,169 @@
+require "json"
+require "pathname"
+require "securerandom"
+
+module Vagrant
+  # MachineIndex is able to manage the index of created Vagrant environments
+  # in a central location.
+  #
+  # The MachineIndex stores a mapping of UUIDs to basic information about
+  # a machine. The UUIDs are stored with the Vagrant environment and are
+  # looked up in the machine index.
+  #
+  # The MachineIndex stores information such as the name of a machine,
+  # the directory it was last seen at, its last known state, etc. Using
+  # this information, we can load the entire {Machine} object for a machine,
+  # or we can just display metadata if needed.
+  #
+  # The internal format of the data file is currently JSON in the following
+  # structure:
+  #
+  #   {
+  #     "version": 1,
+  #     "machines": {
+  #       "uuid": {
+  #         "name": "foo",
+  #         "provider": "vmware_fusion",
+  #         "data_path": "/path/to/data/dir",
+  #         "vagrantfile_path": "/path/to/Vagrantfile",
+  #         "state": "running",
+  #         "updated_at": "2014-03-02 11:11:44 +0100"
+  #       }
+  #     }
+  #   }
+  #
+  class MachineIndex
+    # Initializes a MachineIndex at the given file location.
+    #
+    # @param [Pathname] data_file Path to the file that should be used
+    #   to maintain the machine index. This file doesn't have to exist
+    #   but this location must be writable.
+    def initialize(data_file)
+      @data_file = data_file
+      @machines  = {}
+
+      if @data_file.file?
+        data = nil
+        begin
+          data = JSON.load(@data_file.read)
+        rescue JSON::ParserError
+          raise Errors::CorruptMachineIndex, path: data_file.to_s
+        end
+
+        if data
+          if !data["version"] || data["version"].to_i != 1
+            raise Errors::CorruptMachineIndex, path: data_file.to_s
+          end
+
+          @machines = data["machines"] || {}
+        end
+      end
+    end
+
+    # Accesses a machine by UUID and returns a {MachineIndex::Entry}
+    #
+    # @param [String] uuid UUID for the machine to access.
+    # @return [MachineIndex::Entry]
+    def [](uuid)
+      return nil if !@machines[uuid]
+      Entry.new(uuid, @machines[uuid].merge("id" => uuid))
+    end
+
+    # Creates/updates an entry object and returns the resulting entry.
+    #
+    # If the entry was new (no UUID), then the UUID will be set on the
+    # resulting entry and can be used.
+    #
+    # @param [Entry] entry
+    # @return [Entry]
+    def set(entry)
+      # Get the struct and update the updated_at attribute
+      struct = entry.to_json_struct
+
+      # Set an ID if there isn't one already set
+      id     = entry.id
+      id     ||= SecureRandom.uuid
+
+      # Store the data
+      @machines[id] = struct
+      save
+
+      Entry.new(id, struct)
+    end
+
+    # Saves the index.
+    #
+    # This doesn't usually need to be called because {#set} will
+    # automatically save as well.
+    def save
+      @data_file.open("w") do |f|
+        f.write(JSON.dump({
+          "version"  => 1,
+          "machines" => @machines,
+        }))
+      end
+    end
+
+    # An entry in the MachineIndex.
+    class Entry
+      # The unique ID for this entry. This is _not_ the ID for the
+      # machine itself (which is provider-specific and in the data directory).
+      #
+      # @return [String]
+      attr_reader :id
+
+      # The name of the machine.
+      #
+      # @return [String]
+      attr_accessor :name
+
+      # The name of the provider.
+      #
+      # @return [String]
+      attr_accessor :provider
+
+      # The last known state of this machine.
+      #
+      # @return [String]
+      attr_accessor :state
+
+      # The path to the Vagrantfile that manages this machine.
+      #
+      # @return [Pathname]
+      attr_accessor :vagrantfile_path
+
+      # The last time this entry was updated.
+      #
+      # @return [DateTime]
+      attr_reader :updated_at
+
+      # Initializes an entry.
+      #
+      # The parameter given should be nil if this is being created
+      # publicly.
+      def initialize(id=nil, raw=nil)
+        # Do nothing if we aren't given a raw value. Otherwise, parse it.
+        return if !raw
+
+        @id               = id
+        @name             = raw["name"]
+        @provider         = raw["provider"]
+        @state            = raw["state"]
+        @vagrantfile_path = Pathname.new(raw["vagrantfile_path"])
+        # TODO(mitchellh): parse into a proper datetime
+        @updated_at       = raw["updated_at"]
+      end
+
+      # Converts to the structure used by the JSON
+      def to_json_struct
+        {
+          "name"             => @name,
+          "provider"         => @provider,
+          "state"            => @state,
+          "vagrantfile_path" => @vagrantfile_path,
+          "updated_at"       => @updated_at,
+        }
+      end
+    end
+  end
+end
diff --git a/templates/locales/en.yml b/templates/locales/en.yml
index 8af58badf..b37e29214 100644
--- a/templates/locales/en.yml
+++ b/templates/locales/en.yml
@@ -598,6 +598,18 @@ en:
 
         Source: %{source}
         Destination: %{destination}
+      corrupt_machine_index: |-
+        The machine index which stores all required information about
+        running Vagrant environments has become corrupt. This is usually
+        caused by external tampering of the Vagrant data folder.
+
+        Vagrant cannot manage any Vagrant environments if the index is
+        corrupt. Please attempt to manually correct it. If you are unable
+        to manually correct it, then remove the data file at the path below.
+        This will leave all existing Vagrant environments "orphaned" and
+        they'll have to be destroyed manually.
+
+        Path: %{path}
       destroy_requires_force: |-
         Destroy doesn't have a TTY to ask for confirmation. Please pass the
         `--force` flag to force a destroy, otherwise attach a TTY so that
diff --git a/test/unit/vagrant/machine_directory_test.rb b/test/unit/vagrant/machine_directory_test.rb
new file mode 100644
index 000000000..f401985be
--- /dev/null
+++ b/test/unit/vagrant/machine_directory_test.rb
@@ -0,0 +1,110 @@
+require "json"
+require "pathname"
+require "tempfile"
+
+require File.expand_path("../../base", __FILE__)
+
+require "vagrant/machine_index"
+
+describe Vagrant::MachineIndex do
+  include_context "unit"
+
+  let(:data_file) { temporary_file }
+
+  subject { described_class.new(data_file) }
+
+  it "raises an exception if the data file is corrupt" do
+    data_file.open("w") do |f|
+      f.write(JSON.dump({}))
+    end
+
+    expect { subject }.
+      to raise_error(Vagrant::Errors::CorruptMachineIndex)
+  end
+
+  it "raises an exception if the JSON is invalid" do
+    data_file.open("w") do |f|
+      f.write("foo")
+    end
+
+    expect { subject }.
+      to raise_error(Vagrant::Errors::CorruptMachineIndex)
+  end
+
+  describe "#[]" do
+    before do
+      data = {
+        "version" => 1,
+        "machines" => {
+          "bar" => {
+            "name" => "default",
+            "provider" => "vmware",
+            "vagrantfile_path" => "/foo/bar/baz",
+            "state" => "running",
+            "updated_at" => "foo",
+          }
+        }
+      }
+
+      data_file.open("w") do |f|
+        f.write(JSON.dump(data))
+      end
+    end
+
+    it "returns nil if the machine doesn't exist" do
+      expect(subject["foo"]).to be_nil
+    end
+
+    it "returns a valid entry if the machine exists" do
+      result = subject["bar"]
+
+      expect(result.id).to eq("bar")
+      expect(result.name).to eq("default")
+      expect(result.provider).to eq("vmware")
+      expect(result.vagrantfile_path).to eq(Pathname.new("/foo/bar/baz"))
+      expect(result.state).to eq("running")
+      expect(result.updated_at).to eq("foo")
+    end
+  end
+
+  describe "#set and #[]" do
+    let(:entry_klass) { Vagrant::MachineIndex::Entry }
+
+    it "adds a new entry" do
+      entry = entry_klass.new
+      entry.name = "foo"
+      entry.vagrantfile_path = "/bar"
+
+      result = subject.set(entry)
+      expect(result.id).to_not be_empty
+
+      # Get it froma new class and check the results
+      subject = described_class.new(data_file)
+      entry   = subject[result.id]
+      expect(entry).to_not be_nil
+      expect(entry.name).to eq("foo")
+
+      # TODO: test that updated_at is set
+    end
+
+    it "updates an existing entry" do
+      entry = entry_klass.new
+      entry.name = "foo"
+      entry.vagrantfile_path = "/bar"
+
+      result = subject.set(entry)
+      expect(result.id).to_not be_empty
+
+      result.name = "bar"
+
+      nextresult = subject.set(result)
+      expect(nextresult.id).to eq(result.id)
+
+      # Get it froma new class and check the results
+      subject = described_class.new(data_file)
+      entry   = subject[result.id]
+      expect(entry).to_not be_nil
+      expect(entry.name).to eq("bar")
+    end
+  end
+end