diff --git a/booklist/book.go b/booklist/book.go
index 2b7c607c..97a63669 100644
--- a/booklist/book.go
+++ b/booklist/book.go
@@ -8,6 +8,11 @@ import (
 	"time"
 )
 
+type cachedID struct {
+	id string
+	value string
+}
+
 type Book struct {
 	Hash     string
 	FilePath string
@@ -21,18 +26,30 @@ type Book struct {
 	Series      string
 	SeriesIndex float64
 	Publisher   string
+
+	seriesid	cachedID
+	authorid	cachedID
 }
 
 func (b *Book) ID() string {
 	return b.Hash[:10]
 }
 
+func (b *Book) cachedIDStr(cached *cachedID, value string) string {
+	if len(cached.id)==0 || value != cached.value {
+		cached.value = value
+		cached.id = fmt.Sprintf("%x", sha1.Sum([]byte(value)))[:10]
+	}
+
+	return cached.id
+}
+
 func (b *Book) AuthorID() string {
-	return fmt.Sprintf("%x", sha1.Sum([]byte(b.Author)))[:10]
+	return b.cachedIDStr(&b.authorid,b.Author)
 }
 
 func (b *Book) SeriesID() string {
-	return fmt.Sprintf("%x", sha1.Sum([]byte(b.Series)))[:10]
+	return b.cachedIDStr(&b.seriesid,b.Series)
 }
 
 func (b *Book) FileType() string {