diff --git a/store/codex.go b/store/codex.go
new file mode 100644
index 0000000..8f7226d
--- /dev/null
+++ b/store/codex.go
@@ -0,0 +1,88 @@
+package store
+
+import (
+	"encoding/json"
+
+	bolt "go.etcd.io/bbolt"
+)
+
+var bucketCodex = []byte("codex")
+
+type Codex struct {
+	Monsters map[string]bool `json:"monsters"`
+	Items    map[string]bool `json:"items"`
+	Events   map[string]bool `json:"events"`
+}
+
+func newCodex() Codex {
+	return Codex{
+		Monsters: make(map[string]bool),
+		Items:    make(map[string]bool),
+		Events:   make(map[string]bool),
+	}
+}
+
+func (d *DB) RecordCodexEntry(fingerprint, category, id string) error {
+	return d.db.Update(func(tx *bolt.Tx) error {
+		b := tx.Bucket(bucketCodex)
+		key := []byte(fingerprint)
+		codex := newCodex()
+
+		v := b.Get(key)
+		if v != nil {
+			if err := json.Unmarshal(v, &codex); err != nil {
+				return err
+			}
+			// Ensure maps are initialized after unmarshal
+			if codex.Monsters == nil {
+				codex.Monsters = make(map[string]bool)
+			}
+			if codex.Items == nil {
+				codex.Items = make(map[string]bool)
+			}
+			if codex.Events == nil {
+				codex.Events = make(map[string]bool)
+			}
+		}
+
+		switch category {
+		case "monster":
+			codex.Monsters[id] = true
+		case "item":
+			codex.Items[id] = true
+		case "event":
+			codex.Events[id] = true
+		}
+
+		data, err := json.Marshal(codex)
+		if err != nil {
+			return err
+		}
+		return b.Put(key, data)
+	})
+}
+
+func (d *DB) GetCodex(fingerprint string) (Codex, error) {
+	codex := newCodex()
+	err := d.db.View(func(tx *bolt.Tx) error {
+		b := tx.Bucket(bucketCodex)
+		v := b.Get([]byte(fingerprint))
+		if v == nil {
+			return nil
+		}
+		if err := json.Unmarshal(v, &codex); err != nil {
+			return err
+		}
+		if codex.Monsters == nil {
+			codex.Monsters = make(map[string]bool)
+		}
+		if codex.Items == nil {
+			codex.Items = make(map[string]bool)
+		}
+		if codex.Events == nil {
+			codex.Events = make(map[string]bool)
+		}
+		return nil
+	})
+	return codex, err
+}
diff --git a/store/codex_test.go b/store/codex_test.go
new file mode 100644
index 0000000..65f8de3
--- /dev/null
+++ b/store/codex_test.go
@@ -0,0 +1,71 @@
+package store
+
+import (
+	"testing"
+)
+
+func TestRecordCodexEntry(t *testing.T) {
+	dir := t.TempDir()
+	db, err := Open(dir + "/test_codex.db")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	// Record some entries
+	db.RecordCodexEntry("fp1", "monster", "goblin")
+	db.RecordCodexEntry("fp1", "monster", "skeleton")
+	db.RecordCodexEntry("fp1", "item", "health_potion")
+	db.RecordCodexEntry("fp1", "event", "altar")
+
+	codex, err := db.GetCodex("fp1")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(codex.Monsters) != 2 {
+		t.Errorf("expected 2 monsters, got %d", len(codex.Monsters))
+	}
+	if !codex.Monsters["goblin"] {
+		t.Error("expected goblin in monsters")
+	}
+	if !codex.Monsters["skeleton"] {
+		t.Error("expected skeleton in monsters")
+	}
+	if len(codex.Items) != 1 {
+		t.Errorf("expected 1 item, got %d", len(codex.Items))
+	}
+	if !codex.Items["health_potion"] {
+		t.Error("expected health_potion in items")
+	}
+	if len(codex.Events) != 1 {
+		t.Errorf("expected 1 event, got %d", len(codex.Events))
+	}
+	if !codex.Events["altar"] {
+		t.Error("expected altar in events")
+	}
+
+	// Duplicate entry should not increase count
+	db.RecordCodexEntry("fp1", "monster", "goblin")
+	codex2, _ := db.GetCodex("fp1")
+	if len(codex2.Monsters) != 2 {
+		t.Errorf("expected still 2 monsters after duplicate, got %d", len(codex2.Monsters))
+	}
+}
+
+func TestGetCodexEmpty(t *testing.T) {
+	dir := t.TempDir()
+	db, err := Open(dir + "/test_codex_empty.db")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	codex, err := db.GetCodex("fp_unknown")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(codex.Monsters) != 0 || len(codex.Items) != 0 || len(codex.Events) != 0 {
+		t.Error("expected empty codex for unknown player")
+	}
+}