diff --git a/imageserver/httpd/listDirectories.go b/imageserver/httpd/listDirectories.go
index 4a8f695f..1025dbb5 100644
--- a/imageserver/httpd/listDirectories.go
+++ b/imageserver/httpd/listDirectories.go
@@ -4,6 +4,8 @@ import (
 	"bufio"
 	"fmt"
 	"net/http"
+	"net/url"
+	"text/template"
 
 	"github.com/Cloud-Foundations/Dominator/lib/html"
 	"github.com/Cloud-Foundations/Dominator/lib/image"
@@ -32,8 +34,20 @@ func (s state) listDirectoriesHandler(w http.ResponseWriter,
 	fmt.Fprintln(writer, `<table border="1" style="width:100%">`)
 	tw, _ := html.NewTableWriter(writer, true, "Name", "Owner Group")
 	for _, directory := range directories {
-		tw.WriteRow("", "", directory.Name, directory.Metadata.OwnerGroup)
+		writeDirectory(tw, directory)
 	}
 	tw.Close()
 	fmt.Fprintln(writer, "</body>")
 }
+
+func writeDirectory(tw *html.TableWriter, directory image.Directory) {
+	name := directory.Name
+	ownerGroup := directory.Metadata.OwnerGroup
+	tw.WriteRow("", "",
+		fmt.Sprintf(
+			"<a href=\"listImages?directoryName=%s\">%s</a>",
+			url.QueryEscape(name), template.HTMLEscapeString(name),
+		),
+		ownerGroup,
+	)
+}
diff --git a/imageserver/httpd/listImages.go b/imageserver/httpd/listImages.go
index a375abff..953b115d 100644
--- a/imageserver/httpd/listImages.go
+++ b/imageserver/httpd/listImages.go
@@ -14,9 +14,17 @@ import (
 func (s state) listImagesHandler(w http.ResponseWriter, req *http.Request) {
 	writer := bufio.NewWriter(w)
 	defer writer.Flush()
-	imageNames := s.imageDataBase.ListImages()
-	verstr.Sort(imageNames)
-	if req.URL.RawQuery == "output=text" {
+	query := req.URL.Query()
+	var imageNames []string
+	if directoryName := query.Get("directoryName"); directoryName != "" &&
+		directoryName != "." {
+		// Output is already sorted.
+		imageNames = s.imageDataBase.ListImagesInDirectory(directoryName)
+	} else {
+		imageNames = s.imageDataBase.ListImages()
+		verstr.Sort(imageNames)
+	}
+	if query.Get("output") == "text" {
 		for _, name := range imageNames {
 			fmt.Fprintln(writer, name)
 		}
diff --git a/imageserver/scanner/api.go b/imageserver/scanner/api.go
index a9f42ce2..27067ec5 100644
--- a/imageserver/scanner/api.go
+++ b/imageserver/scanner/api.go
@@ -30,6 +30,7 @@ type Config struct {
 }
 
 type notifiers map[<-chan string]chan<- string
+
 type makeDirectoryNotifiers map[<-chan image.Directory]chan<- image.Directory
 
 type ImageDataBase struct {
@@ -42,6 +43,7 @@ type ImageDataBase struct {
 	// Protected by main lock.
 	directoryMap    map[string]image.DirectoryMetadata
 	imageMap        map[string]*imageType // nil: write in progress.
+	imageNameIndex  imageIndex            // sorted keys of image names.
 	addNotifiers    notifiers
 	deleteNotifiers notifiers
 	mkdirNotifiers  makeDirectoryNotifiers
@@ -64,6 +66,16 @@ type Params struct {
 	ObjectServer objectserver.FullObjectServer
 }
 
+// imageIndex provides exact and prefix lookups over image names.
+// Implementations are not safe for concurrent use; callers must hold the
+// main lock.
+type imageIndex interface {
+	Add(name string)
+	Delete(name string)
+	Get(name string) (string, bool)
+	GetByPrefix(prefix string) []string
+}
+
 func Load(config Config, params Params) (*ImageDataBase, error) {
 	return loadImageDataBase(config, params)
 }
@@ -187,6 +199,11 @@ func (imdb *ImageDataBase) ListSelectedImages(
 	return imdb.listImages(request)
 }
 
+func (imdb *ImageDataBase) ListImagesInDirectory(
+	directoryName string) []string {
+	return imdb.listImagesInDirectory(directoryName)
+}
+
 // ListUnreferencedObjects will return a map listing all the objects and their
 // corresponding sizes which are not referenced by an image.
 // Note that some objects may have been recently added and the referencing image
diff --git a/imageserver/scanner/imdb.go b/imageserver/scanner/imdb.go
index d413c915..383d3cca 100644
--- a/imageserver/scanner/imdb.go
+++ b/imageserver/scanner/imdb.go
@@ -92,6 +92,7 @@ func (imdb *ImageDataBase) addImage(img *image.Image, name string,
 		if doCleanup {
 			imdb.Lock()
 			delete(imdb.imageMap, name)
+			imdb.imageNameIndex.Delete(name)
 			imdb.Unlock()
 		}
 	}()
@@ -392,6 +393,7 @@ func (imdb *ImageDataBase) deleteImageAndUpdateUnreferencedObjectsList(
 		return
 	}
 	delete(imdb.imageMap, name)
+	imdb.imageNameIndex.Delete(name)
 	imdb.Params.ObjectServer.AdjustRefcounts(false, img)
 }
 
@@ -612,6 +614,13 @@ func (imdb *ImageDataBase) listImages(
 	return names
 }
 
+func (imdb *ImageDataBase) listImagesInDirectory(
+	directoryName string) []string {
+	imdb.RLock()
+	defer imdb.RUnlock()
+	return imdb.imageNameIndex.GetByPrefix(directoryName)
+}
+
 func (imdb *ImageDataBase) makeDirectory(directory image.Directory,
 	authInfo *srpc.AuthInformation, userRpc bool) error {
 	imdb.Lock()
@@ -743,6 +752,7 @@ func (imdb *ImageDataBase) restoreImageFromArchive(
 		if doCleanup {
 			imdb.Lock()
 			delete(imdb.imageMap, imageArchive.ImageName)
+			imdb.imageNameIndex.Delete(imageArchive.ImageName)
 			imdb.Unlock()
 		}
 	}()
@@ -814,6 +824,7 @@ func (imdb *ImageDataBase) writeImage(name string, img *image.Image,
 		usageEstimate: usageEstimate,
 	}
 	imdb.addNotifiers.sendPlain(name, "add", imdb.Logger)
+	imdb.imageNameIndex.Add(name)
 	imdb.Unlock()
 	return imdb.Params.ObjectServer.AdjustRefcounts(true, img)
 }
diff --git a/imageserver/scanner/index.go b/imageserver/scanner/index.go
new file mode 100644
index 00000000..727fe5fd
--- /dev/null
+++ b/imageserver/scanner/index.go
@@ -0,0 +1,62 @@
+package scanner
+
+import (
+	"slices"
+	"strings"
+)
+
+// sortedImageIndex is an imageIndex backed by a sorted slice of image names.
+type sortedImageIndex struct {
+	index []string // sorted image names only.
+}
+
+func newImageSortedIndex() *sortedImageIndex {
+	return &sortedImageIndex{index: make([]string, 0)}
+}
+
+var _ imageIndex = &sortedImageIndex{}
+
+func (s *sortedImageIndex) Add(name string) {
+	i, found := slices.BinarySearch(s.index, name)
+	if found {
+		return
+	}
+	s.index = slices.Insert(s.index, i, name)
+}
+
+func (s *sortedImageIndex) Delete(name string) {
+	i, found := slices.BinarySearch(s.index, name)
+	if !found {
+		return
+	}
+	s.index = slices.Delete(s.index, i, i+1)
+}
+
+func (s *sortedImageIndex) GetByPrefix(prefix string) []string {
+	if !strings.HasSuffix(prefix, "/") {
+		prefix += "/"
+	}
+	start, _ := slices.BinarySearch(s.index, prefix)
+	if start == len(s.index) || !strings.HasPrefix(s.index[start], prefix) {
+		return nil
+	}
+	relativeEnd, _ := slices.BinarySearchFunc(s.index[start:], prefix,
+		func(e, t string) int {
+			if strings.HasPrefix(e, t) {
+				// Move the search outside of prefix block.
+				return -1
+			}
+			return strings.Compare(e, t)
+		},
+	)
+	end := start + relativeEnd
+	return slices.Clone(s.index[start:end])
+}
+
+func (s *sortedImageIndex) Get(name string) (string, bool) {
+	i, found := slices.BinarySearch(s.index, name)
+	if !found {
+		return "", false
+	}
+	return s.index[i], true
+}
diff --git a/imageserver/scanner/load.go b/imageserver/scanner/load.go
index cdd63708..47514174 100644
--- a/imageserver/scanner/load.go
+++ b/imageserver/scanner/load.go
@@ -46,6 +46,7 @@ func loadImageDataBase(config Config, params Params) (*ImageDataBase, error) {
 		Params:          params,
 		directoryMap:    make(map[string]image.DirectoryMetadata),
 		imageMap:        make(map[string]*imageType),
+		imageNameIndex:  newImageSortedIndex(),
 		addNotifiers:    make(notifiers),
 		deleteNotifiers: make(notifiers),
 		mkdirNotifiers:  make(makeDirectoryNotifiers),
@@ -200,6 +201,7 @@ func (imdb *ImageDataBase) loadFile(filename string) error {
 	imdb.Lock()
 	defer imdb.Unlock()
 	imdb.imageMap[filename] = imageEntry
+	imdb.imageNameIndex.Add(filename)
 	return nil
 }