diff --git a/hook/hook.go b/hook/hook.go
index 51750dbc..6bc909d8 100644
--- a/hook/hook.go
+++ b/hook/hook.go
@@ -3,14 +3,22 @@
 package hook
 
 import (
+	"io"
 	"os"
 
 	"asdf/config"
 	"asdf/execute"
 )
 
-// Run gets a hook command from config and runs it with the provided arguments
-func Run(config config.Config, hookName string, arguments []string) error {
+// Run gets a hook command from config and runs it with the provided arguments.
+// Output is sent to STDOUT and STDERR
+func Run(conf config.Config, hookName string, arguments []string) error {
+	return RunWithOutput(conf, hookName, arguments, os.Stdout, os.Stderr)
+}
+
+// RunWithOutput gets a hook command from config and runs it with the provided
+// arguments. Output is sent to the provided io.Writers.
+func RunWithOutput(config config.Config, hookName string, arguments []string, stdOut io.Writer, stdErr io.Writer) error {
 	hookCmd, err := config.GetHook(hookName)
 	if err != nil {
 		return err
@@ -22,8 +30,8 @@ func Run(config config.Config, hookName string, arguments []string) error {
 
 	cmd := execute.NewExpression(hookCmd, arguments)
 
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
+	cmd.Stdout = stdOut
+	cmd.Stderr = stdErr
 
 	return cmd.Run()
 }
diff --git a/internal/resolve/testdata/asdfrc b/internal/resolve/testdata/asdfrc
new file mode 100644
index 00000000..e600bd0c
--- /dev/null
+++ b/internal/resolve/testdata/asdfrc
@@ -0,0 +1 @@
+legacy_version_file = yes
diff --git a/internal/versions/testdata/asdfrc b/internal/versions/testdata/asdfrc
new file mode 100644
index 00000000..dfa93fb6
--- /dev/null
+++ b/internal/versions/testdata/asdfrc
@@ -0,0 +1,3 @@
+pre_asdf_download_lua = echo pre_asdf_download_lua $@
+pre_asdf_install_lua = echo pre_asdf_install_lua $@
+post_asdf_install_lua = echo post_asdf_install_lua $@
diff --git a/internal/versions/versions.go b/internal/versions/versions.go
new file mode 100644
index 00000000..ed1dbb9f
--- /dev/null
+++ b/internal/versions/versions.go
@@ -0,0 +1,126 @@
+// Package versions handles all operations pertaining to specific versions.
+// Install, uninstall, etc...
+package versions
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"asdf/config"
+	"asdf/hook"
+	"asdf/plugins"
+)
+
+const (
+	systemVersion           = "system"
+	latestVersion           = "latest"
+	uninstallableVersionMsg = "uninstallable version: system"
+	dataDirDownloads        = "downloads"
+	dataDirInstalls         = "installs"
+)
+
+// UninstallableVersion is an error returned if someone tries to install the
+// system version.
+type UninstallableVersion struct{}
+
+func (e UninstallableVersion) Error() string {
+	return fmt.Sprint(uninstallableVersionMsg)
+}
+
+// TODO: Implement these functions
+//func InstallAll() {
+//}
+
+//func InstallOne() {
+//}
+
+// InstallOneVersion installs a specific version of a specific tool
+func InstallOneVersion(conf config.Config, plugin plugins.Plugin, version string, _ bool, stdOut io.Writer, stdErr io.Writer) error {
+	err := plugin.Exists()
+	if err != nil {
+		return err
+	}
+
+	if version == systemVersion {
+		return UninstallableVersion{}
+	}
+
+	if version == latestVersion {
+		// TODO: Implement this
+		return errors.New("not implemented")
+	}
+
+	downloadDir := downloadPath(conf, plugin, version)
+	installDir := installPath(conf, plugin, version)
+	versionType, version := ParseString(version)
+
+	// Check if version already installed
+	if _, err = os.Stat(installDir); !os.IsNotExist(err) {
+		return fmt.Errorf("version %s of %s is already installed", version, plugin.Name)
+	}
+
+	env := map[string]string{
+		"ASDF_INSTALL_TYPE":    versionType,
+		"ASDF_INSTALL_VERSION": version,
+		"ASDF_INSTALL_PATH":    installDir,
+		"ASDF_DOWNLOAD_PATH":   downloadDir,
+	}
+
+	err = os.MkdirAll(downloadDir, 0o777)
+	if err != nil {
+		return fmt.Errorf("unable to create download dir: %w", err)
+	}
+
+	err = hook.RunWithOutput(conf, fmt.Sprintf("pre_asdf_download_%s", plugin.Name), []string{version}, stdOut, stdErr)
+	if err != nil {
+		return fmt.Errorf("failed to run pre-download hook: %w", err)
+	}
+
+	err = plugin.RunCallback("download", []string{}, env, stdOut, stdErr)
+	if _, ok := err.(plugins.NoCallbackError); err != nil && !ok {
+		return fmt.Errorf("failed to run download callback: %w", err)
+	}
+
+	err = hook.RunWithOutput(conf, fmt.Sprintf("pre_asdf_install_%s", plugin.Name), []string{version}, stdOut, stdErr)
+	if err != nil {
+		return fmt.Errorf("failed to run pre-install hook: %w", err)
+	}
+
+	err = os.MkdirAll(installDir, 0o777)
+	if err != nil {
+		return fmt.Errorf("unable to create install dir: %w", err)
+	}
+
+	err = plugin.RunCallback("install", []string{}, env, stdOut, stdErr)
+	if err != nil {
+		return fmt.Errorf("failed to run install callback: %w", err)
+	}
+
+	err = hook.RunWithOutput(conf, fmt.Sprintf("post_asdf_install_%s", plugin.Name), []string{version}, stdOut, stdErr)
+	if err != nil {
+		return fmt.Errorf("failed to run post-install hook: %w", err)
+	}
+	return nil
+}
+
+func downloadPath(conf config.Config, plugin plugins.Plugin, version string) string {
+	return filepath.Join(conf.DataDir, dataDirDownloads, plugin.Name, version)
+}
+
+func installPath(conf config.Config, plugin plugins.Plugin, version string) string {
+	return filepath.Join(conf.DataDir, dataDirInstalls, plugin.Name, version)
+}
+
+// ParseString parses a version string into versionType and version components
+func ParseString(version string) (string, string) {
+	segments := strings.Split(version, ":")
+	if len(segments) >= 1 && segments[0] == "ref" {
+		return "ref", strings.Join(segments[1:], ":")
+	}
+
+	return "version", version
+}
diff --git a/internal/versions/versions_test.go b/internal/versions/versions_test.go
new file mode 100644
index 00000000..5a9d4e99
--- /dev/null
+++ b/internal/versions/versions_test.go
@@ -0,0 +1,194 @@
+package versions
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"asdf/config"
+	"asdf/plugins"
+	"asdf/repotest"
+
+	"github.com/stretchr/testify/assert"
+)
+
+const testPluginName = "lua"
+
+func TestInstallOneVersion(t *testing.T) {
+	t.Setenv("ASDF_CONFIG_FILE", "testdata/asdfrc")
+
+	t.Run("returns error when plugin doesn't exist", func(t *testing.T) {
+		conf, _ := generateConfig(t)
+		stdout, stderr := buildOutputs()
+		err := InstallOneVersion(conf, plugins.New(conf, "non-existent"), "1.2.3", false, &stdout, &stderr)
+		assert.IsType(t, plugins.PluginMissing{}, err)
+	})
+
+	t.Run("returns error when plugin version is 'system'", func(t *testing.T) {
+		conf, plugin := generateConfig(t)
+		stdout, stderr := buildOutputs()
+		err := InstallOneVersion(conf, plugin, "system", false, &stdout, &stderr)
+		assert.IsType(t, UninstallableVersion{}, err)
+	})
+
+	//t.Run("installs latest version of tool when version is 'latest'", func(t *testing.T) {
+	//  t.Fatal("not implemented")
+	//})
+
+	t.Run("returns error when version doesn't exist", func(t *testing.T) {
+		version := "other-dummy"
+		conf, plugin := generateConfig(t)
+		stdout, stderr := buildOutputs()
+		err := InstallOneVersion(conf, plugin, version, false, &stdout, &stderr)
+		assert.Errorf(t, err, "failed to run install callback: exit status 1")
+
+		want := "pre_asdf_download_lua other-dummy\npre_asdf_install_lua other-dummy\nDummy couldn't install version: other-dummy (on purpose)\n"
+		assert.Equal(t, want, stdout.String())
+
+		assertNotInstalled(t, conf.DataDir, plugin.Name, version)
+	})
+
+	t.Run("returns error when version already installed", func(t *testing.T) {
+		conf, plugin := generateConfig(t)
+		stdout, stderr := buildOutputs()
+		err := InstallOneVersion(conf, plugin, "1.0.0", false, &stdout, &stderr)
+		assert.Nil(t, err)
+		assertInstalled(t, conf.DataDir, plugin.Name, "1.0.0")
+
+		// Install a second time
+		err = InstallOneVersion(conf, plugin, "1.0.0", false, &stdout, &stderr)
+		assert.NotNil(t, err)
+	})
+
+	t.Run("creates download directory", func(t *testing.T) {
+		conf, plugin := generateConfig(t)
+		stdout, stderr := buildOutputs()
+		err := InstallOneVersion(conf, plugin, "1.0.0", false, &stdout, &stderr)
+		assert.Nil(t, err)
+
+		downloadPath := filepath.Join(conf.DataDir, "downloads", plugin.Name, "1.0.0")
+		pathInfo, err := os.Stat(downloadPath)
+		assert.Nil(t, err)
+		assert.True(t, pathInfo.IsDir())
+	})
+
+	t.Run("creates install directory", func(t *testing.T) {
+		conf, plugin := generateConfig(t)
+		stdout, stderr := buildOutputs()
+		err := InstallOneVersion(conf, plugin, "1.0.0", false, &stdout, &stderr)
+		assert.Nil(t, err)
+
+		installPath := filepath.Join(conf.DataDir, "installs", plugin.Name, "1.0.0")
+		pathInfo, err := os.Stat(installPath)
+		assert.Nil(t, err)
+		assert.True(t, pathInfo.IsDir())
+	})
+
+	t.Run("runs pre-download, pre-install and post-install hooks when installation successful", func(t *testing.T) {
+		conf, plugin := generateConfig(t)
+		stdout, stderr := buildOutputs()
+		err := InstallOneVersion(conf, plugin, "1.0.0", false, &stdout, &stderr)
+		assert.Nil(t, err)
+		assert.Equal(t, "", stderr.String())
+		want := "pre_asdf_download_lua 1.0.0\npre_asdf_install_lua 1.0.0\npost_asdf_install_lua 1.0.0\n"
+		assert.Equal(t, want, stdout.String())
+	})
+
+	t.Run("installs successfully when plugin exists but version does not", func(t *testing.T) {
+		conf, plugin := generateConfig(t)
+		stdout, stderr := buildOutputs()
+		err := InstallOneVersion(conf, plugin, "1.0.0", false, &stdout, &stderr)
+		assert.Nil(t, err)
+
+		// Check download directory
+		downloadPath := filepath.Join(conf.DataDir, "downloads", plugin.Name, "1.0.0")
+		entries, err := os.ReadDir(downloadPath)
+		assert.Nil(t, err)
+		// mock plugin doesn't write anything
+		assert.Empty(t, entries)
+
+		// Check install directory
+		assertInstalled(t, conf.DataDir, plugin.Name, "1.0.0")
+	})
+
+	t.Run("install successfully when plugin lacks download callback", func(t *testing.T) {
+		conf, _ := generateConfig(t)
+		stdout, stderr := buildOutputs()
+		testPluginName := "no-download"
+		_, err := repotest.InstallPlugin("dummy_plugin_no_download", conf.DataDir, testPluginName)
+		assert.Nil(t, err)
+		plugin := plugins.New(conf, testPluginName)
+
+		err = InstallOneVersion(conf, plugin, "1.0.0", false, &stdout, &stderr)
+		assert.Nil(t, err)
+
+		// no-download install script prints 'install'
+		assert.Equal(t, "install", stdout.String())
+	})
+}
+
+func TestParseString(t *testing.T) {
+	t.Run("returns 'version', and unmodified version when passed semantic version", func(t *testing.T) {
+		versionType, version := ParseString("1.2.3")
+		assert.Equal(t, versionType, "version")
+		assert.Equal(t, version, "1.2.3")
+	})
+
+	t.Run("returns 'ref' and reference version when passed a ref version", func(t *testing.T) {
+		versionType, version := ParseString("ref:abc123")
+		assert.Equal(t, versionType, "ref")
+		assert.Equal(t, version, "abc123")
+	})
+
+	t.Run("returns 'ref' and empty string when passed 'ref:'", func(t *testing.T) {
+		versionType, version := ParseString("ref:")
+		assert.Equal(t, versionType, "ref")
+		assert.Equal(t, version, "")
+	})
+}
+
+// Helper functions
+func buildOutputs() (strings.Builder, strings.Builder) {
+	var stdout strings.Builder
+	var stderr strings.Builder
+
+	return stdout, stderr
+}
+
+func assertInstalled(t *testing.T, dataDir, pluginName, version string) {
+	t.Helper()
+
+	installPath := filepath.Join(dataDir, "installs", pluginName, version)
+	entries, err := os.ReadDir(installPath)
+	assert.Nil(t, err)
+
+	var fileNames []string
+	for _, e := range entries {
+		fileNames = append(fileNames, e.Name())
+	}
+
+	assert.Equal(t, fileNames, []string{"bin", "env", "version"})
+}
+
+func assertNotInstalled(t *testing.T, dataDir, pluginName, version string) {
+	t.Helper()
+
+	installPath := filepath.Join(dataDir, "installs", pluginName, version)
+	entries, err := os.ReadDir(installPath)
+	assert.Empty(t, entries)
+	assert.Nil(t, err)
+}
+
+func generateConfig(t *testing.T) (config.Config, plugins.Plugin) {
+	t.Helper()
+	testDataDir := t.TempDir()
+	conf, err := config.LoadConfig()
+	assert.Nil(t, err)
+	conf.DataDir = testDataDir
+
+	_, err = repotest.InstallPlugin("dummy_plugin", testDataDir, testPluginName)
+	assert.Nil(t, err)
+
+	return conf, plugins.New(conf, testPluginName)
+}
diff --git a/plugins/plugins.go b/plugins/plugins.go
index e84bfcf3..c13e46dd 100644
--- a/plugins/plugins.go
+++ b/plugins/plugins.go
@@ -33,6 +33,16 @@ func (e PluginAlreadyExists) Error() string {
 	return fmt.Sprintf(pluginAlreadyExistsMsg, e.plugin)
 }
 
+// PluginMissing is the error returned when Plugin.Exists is call and the plugin
+// doesn't exist on disk.
+type PluginMissing struct {
+	plugin string
+}
+
+func (e PluginMissing) Error() string {
+	return fmt.Sprintf(pluginMissingMsg, e.plugin)
+}
+
 // NoCallbackError is an error returned by RunCallback when a callback with
 // particular name does not exist
 type NoCallbackError struct {
@@ -48,6 +58,7 @@ const (
 	dataDirPlugins         = "plugins"
 	invalidPluginNameMsg   = "%s is invalid. Name may only contain lowercase letters, numbers, '_', and '-'"
 	pluginAlreadyExistsMsg = "Plugin named %s already added"
+	pluginMissingMsg       = "Plugin named %s not installed"
 	hasNoCallbackMsg       = "Plugin named %s does not have a callback named %s"
 )
 
@@ -126,6 +137,20 @@ func (p Plugin) ParseLegacyVersionFile(path string) (versions []string, err erro
 	return versions, err
 }
 
+// Exists returns a boolean indicating whether or not the plugin exists on disk.
+func (p Plugin) Exists() error {
+	exists, err := directoryExists(p.Dir)
+	if err != nil {
+		return err
+	}
+
+	if !exists {
+		return PluginMissing{plugin: p.Name}
+	}
+
+	return nil
+}
+
 // RunCallback invokes a callback with the given name if it exists for the plugin
 func (p Plugin) RunCallback(name string, arguments []string, environment map[string]string, stdOut io.Writer, errOut io.Writer) error {
 	callback := filepath.Join(p.Dir, "bin", name)
diff --git a/plugins/plugins_test.go b/plugins/plugins_test.go
index a3f9e2c6..29fd0763 100644
--- a/plugins/plugins_test.go
+++ b/plugins/plugins_test.go
@@ -285,6 +285,26 @@ func TestUpdate(t *testing.T) {
 	}
 }
 
+func TestExists(t *testing.T) {
+	testDataDir := t.TempDir()
+	conf := config.Config{DataDir: testDataDir}
+	_, err := repotest.InstallPlugin("dummy_plugin", testDataDir, testPluginName)
+	assert.Nil(t, err)
+
+	existingPlugin := New(conf, testPluginName)
+
+	t.Run("returns nil if plugin exists", func(t *testing.T) {
+		err := existingPlugin.Exists()
+		assert.Nil(t, err)
+	})
+
+	t.Run("returns PluginMissing error when plugin missing", func(t *testing.T) {
+		missingPlugin := New(conf, "non-existent")
+		err := missingPlugin.Exists()
+		assert.Equal(t, err, PluginMissing{plugin: "non-existent"})
+	})
+}
+
 func TestPluginExists(t *testing.T) {
 	testDataDir := t.TempDir()
 	pluginDir := PluginDirectory(testDataDir, testPluginName)
@@ -368,10 +388,9 @@ func TestRunCallback(t *testing.T) {
 
 	testDataDir := t.TempDir()
 	conf := config.Config{DataDir: testDataDir}
-	testRepo, err := repotest.GeneratePlugin("dummy_plugin", testDataDir, testPluginName)
+	_, err := repotest.InstallPlugin("dummy_plugin", testDataDir, testPluginName)
 	assert.Nil(t, err)
 
-	err = Add(conf, testPluginName, testRepo)
 	plugin := New(conf, testPluginName)
 
 	t.Run("returns NoCallback error when callback with name not found", func(t *testing.T) {