diff --git a/app/src/main/java/it/danieleverducci/lunatracker/MainActivity.kt b/app/src/main/java/it/danieleverducci/lunatracker/MainActivity.kt
index c6af54e..0e71df2 100644
--- a/app/src/main/java/it/danieleverducci/lunatracker/MainActivity.kt
+++ b/app/src/main/java/it/danieleverducci/lunatracker/MainActivity.kt
@@ -6,17 +6,23 @@ import android.view.View
 import android.widget.NumberPicker
 import androidx.appcompat.app.AlertDialog
 import androidx.appcompat.app.AppCompatActivity
+import it.danieleverducci.lunatracker.entities.Logbook
 import it.danieleverducci.lunatracker.entities.LunaEvent
 import it.danieleverducci.lunatracker.entities.LunaEventType
+import java.io.File
 
 class MainActivity : AppCompatActivity() {
     companion object {
         val TAG = "MainActivity"
     }
 
+    lateinit var logbook: Logbook
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
 
+        logbook = Logbook.load(this)
+
         setContentView(R.layout.activity_main)
 
         findViewById<View>(R.id.button_bottle).setOnClickListener { askBabyBottleContent() }
@@ -68,7 +74,8 @@ class MainActivity : AppCompatActivity() {
     }
 
     fun logEvent(event: LunaEvent) {
-        Log.d(TAG, event.toString())
+        logbook.logs.add(event)
+        logbook.save(this)
     }
 
 }
diff --git a/app/src/main/java/it/danieleverducci/lunatracker/entities/Logbook.kt b/app/src/main/java/it/danieleverducci/lunatracker/entities/Logbook.kt
new file mode 100644
index 0000000..8985a91
--- /dev/null
+++ b/app/src/main/java/it/danieleverducci/lunatracker/entities/Logbook.kt
@@ -0,0 +1,42 @@
+package it.danieleverducci.lunatracker.entities
+
+import android.content.Context
+import android.util.Log
+import org.json.JSONArray
+import java.io.File
+import java.io.FileInputStream
+import java.io.FileNotFoundException
+
+class Logbook {
+    companion object {
+        val TAG = "Logbook"
+
+        fun load(context: Context): Logbook {
+            val logbook = Logbook()
+            val file = File(context.getFilesDir(), "data.json")
+            try {
+                val json = FileInputStream(file).bufferedReader().use { it.readText() }
+                val ja = JSONArray(json)
+                for (i in 0 until ja.length()) {
+                    val jo = ja.getJSONObject(i)
+                    val evt = LunaEvent.fromJson(jo)
+                    logbook.logs.add(evt)
+                }
+            } catch (e: FileNotFoundException) {
+                Log.d(TAG, "No logbook file found")
+            }
+            return logbook
+        }
+    }
+
+    val logs = ArrayList<LunaEvent>()
+
+    fun save(context: Context) {
+        val file = File(context.getFilesDir(), "data.json")
+        val ja = JSONArray()
+        for (l in logs) {
+            ja.put(l.toJson())
+        }
+        file.writeText(ja.toString())
+    }
+}
\ No newline at end of file
diff --git a/app/src/main/java/it/danieleverducci/lunatracker/entities/LunaEvent.kt b/app/src/main/java/it/danieleverducci/lunatracker/entities/LunaEvent.kt
index aa852ff..5e36b80 100644
--- a/app/src/main/java/it/danieleverducci/lunatracker/entities/LunaEvent.kt
+++ b/app/src/main/java/it/danieleverducci/lunatracker/entities/LunaEvent.kt
@@ -1,12 +1,13 @@
 package it.danieleverducci.lunatracker.entities
 
+import org.json.JSONObject
 import java.util.Date
 
 class LunaEvent(
     val type: LunaEventType,
-    val quantity: Int? = null
+    val quantity: Int? = null,
 ){
-    val time: Long  // In unix time (seconds since 1970)
+    var time: Long  // In unix time (seconds since 1970)
 
     init {
         time = System.currentTimeMillis() / 1000
@@ -15,7 +16,43 @@ class LunaEvent(
     override fun toString(): String {
         return "${type.toString()} qty: $quantity time: ${Date(time * 1000)}"
     }
-}
+
+    fun toJson(): JSONObject {
+        val jo = JSONObject()
+        val type = when (type) {
+            LunaEventType.BABY_BOTTLE -> "BABY_BOTTLE"
+            LunaEventType.BREASTFEEDING_LEFT_NIPPLE -> "BREASTFEEDING_LEFT_NIPPLE"
+            LunaEventType.BREASTFEEDING_BOTH_NIPPLE -> "BREASTFEEDING_BOTH_NIPPLE"
+            LunaEventType.BREASTFEEDING_RIGHT_NIPPLE -> "BREASTFEEDING_RIGHT_NIPPLE"
+            LunaEventType.DIAPERCHANGE_POO -> "DIAPERCHANGE_POO"
+            LunaEventType.DIAPERCHANGE_PEE -> "DIAPERCHANGE_PEE"
+            else -> "UNKNOWN"
+        }
+        jo.put("type", type)
+        jo.put("quantity", quantity)
+        jo.put("time", time)
+        return jo
+    }
+
+    companion object {
+        fun fromJson(j: JSONObject): LunaEvent {
+            val type = when (j.getString("type")) {
+                "BABY_BOTTLE" -> LunaEventType.BABY_BOTTLE
+                "BREASTFEEDING_LEFT_NIPPLE" -> LunaEventType.BREASTFEEDING_LEFT_NIPPLE
+                "BREASTFEEDING_BOTH_NIPPLE" -> LunaEventType.BREASTFEEDING_BOTH_NIPPLE
+                "BREASTFEEDING_RIGHT_NIPPLE" -> LunaEventType.BREASTFEEDING_RIGHT_NIPPLE
+                "DIAPERCHANGE_POO" -> LunaEventType.DIAPERCHANGE_POO
+                "DIAPERCHANGE_PEE" -> LunaEventType.DIAPERCHANGE_PEE
+                else -> LunaEventType.UNKNOWN
+            }
+            val quantity = j.optInt("quantity")
+            val time = j.getLong("time")
+            val evt = LunaEvent(type, quantity)
+            evt.time = time
+            return  evt
+        }
+    }
+ }
 
 enum class LunaEventType {
     BABY_BOTTLE,
@@ -24,4 +61,5 @@ enum class LunaEventType {
     BREASTFEEDING_RIGHT_NIPPLE,
     DIAPERCHANGE_POO,
     DIAPERCHANGE_PEE,
+    UNKNOWN
 }
\ No newline at end of file