diff --git a/Collection-Storage.md b/Collection-Storage.md
new file mode 100644
index 0000000..a2b69e1
--- /dev/null
+++ b/Collection-Storage.md
@@ -0,0 +1,43 @@
+# Radicale >= 3.0.0
+
+Collection on storage is always a directory containing
+
+## Files: *.ics / *.vcf
+
+| **Collection Type** | **Files** |
+|-|-|
+| VCALENDAR | *.ics |
+| VADDRESSBOOK | *.vcf |
+
+## File: .Radicale.props
+
+Property file of collection
+
+Example using `jq` for pretty-print
+
+```
+jq . .Radicale.props 
+{
+  "C:calendar-description": "Schedules",
+  "C:supported-calendar-component-set": "VEVENT,VJOURNAL,VTODO",
+  "D:displayname": "Schedules",
+  "ICAL:calendar-color": "#ffc000ff",
+  "tag": "VCALENDAR"
+}
+```
+
+## Directory: .Radicale.cache
+
+### Directory: .Radicale.cache/history
+
+(TODO)
+
+### Directory: .Radicale.cache/item
+
+(TODO)
+
+### Directory: .Radicale.cache/sync-token
+
+(TODO)
+
+