diff --git a/src/ledger.rs b/src/ledger.rs
index a141c1c40..a3c291f26 100644
--- a/src/ledger.rs
+++ b/src/ledger.rs
@@ -1,64 +1,154 @@
 //! The `ledger` module provides functions for parallel verification of the
 //! Proof of History ledger.
 
-use bincode::{deserialize, serialize_into};
+use bincode::{deserialize, deserialize_from, serialize_into};
 use entry::Entry;
 use hash::Hash;
 use packet::{self, SharedBlob, BLOB_DATA_SIZE};
 use rayon::prelude::*;
 use result::{Error, Result};
 use std::collections::VecDeque;
-use std::io::Cursor;
+use std::fs::{create_dir_all, File, OpenOptions};
+use std::io;
+use std::io::prelude::*;
+use std::io::{Cursor, ErrorKind, Seek, SeekFrom};
+use std::mem::size_of;
+use std::path::Path;
 use transaction::Transaction;
-use std::fs::{File, OpenOptions};
 
-// ledger 
-pub struct Ledger{
-    entry_len_len: usize;
-    
-    entry_height: u64; // current index
+// ledger window
+pub struct LedgerWindow {
+    index: File,
+    data: File,
+}
 
-    pub struct Files {
-        index: File; // an array of usize elements
-        data:  File; // concatenated entries
+impl LedgerWindow {
+    // opens a Ledger in directory, provides "infinite" window
+    pub fn new(directory: String) -> io::Result<Self> {
+        let directory = Path::new(&directory);
+
+        let index = File::open(directory.join("index"))?;
+        let data = File::open(directory.join("data"))?;
+
+        Ok(LedgerWindow { index, data })
     }
 
-    reader: Files;
-    writer: Files;
+    pub fn get_entry(&mut self, index: u64) -> io::Result<Entry> {
+        fn u64_at(file: &mut File, at: u64) -> io::Result<u64> {
+            file.seek(SeekFrom::Start(at))?;
+            deserialize_from(file.take(size_of::<u64>() as u64))
+                .map_err(|e| io::Error::new(ErrorKind::Other, e.to_string()))
+        }
 
-    pub fn new(directory: String) -> Self {
-        
-    }
+        let end_offset = u64_at(&mut self.index, index * size_of::<u64>() as u64)?;
 
-    pub fn get_entry_height(&self) -> u64 {
-        entry_height
-    }
-    
-    pub fn entry_at(&self, index: u64) -> Result<Entry> {
-        
-    }
-    pub fn append_entry(&self, entry: &Entry) -> io::Result<u64> {
-        Ok(0)
-    }
-    pub fn append_entries(&self, entries: &[Entry]) -> io::Result<u64> {
-       Ok(0)
+        let start_offset = if index != 0 {
+            u64_at(&mut self.index, (index - 1) * size_of::<u64>() as u64)?
+        } else {
+            0u64
+        };
+
+        fn entry_at(file: &mut File, at: u64, len: u64) -> io::Result<Entry> {
+            file.seek(SeekFrom::Start(at))?;
+
+            deserialize_from(file.take(len))
+                .map_err(|e| io::Error::new(ErrorKind::Other, e.to_string()))
+        }
+
+        entry_at(&mut self.data, start_offset, end_offset - start_offset)
     }
 }
 
-impl<R: BufRead> Iterator for Ledger<R> {
+pub struct LedgerWriter {
+    index: File,
+    data: File,
+}
+
+impl LedgerWriter {
+    // opens or creates a LedgerWriter in directory
+    pub fn new(directory: String) -> io::Result<Self> {
+        let directory = Path::new(&directory);
+
+        create_dir_all(directory)?;
+
+        let index = OpenOptions::new()
+            .create(true)
+            .append(true)
+            .open(directory.join("index"))?;
+
+        let data = OpenOptions::new()
+            .create(true)
+            .append(true)
+            .open(directory.join("data"))?;
+
+        Ok(LedgerWriter { index, data })
+    }
+
+    fn write_entry(&mut self, entry: &Entry) -> io::Result<()> {
+        serialize_into(&mut self.data, &entry)
+            .map_err(|e| io::Error::new(ErrorKind::Other, e.to_string()))?;
+        self.data.flush()?;
+
+        let offset = self.data.seek(SeekFrom::Current(0))?;
+        serialize_into(&mut self.index, &offset)
+            .map_err(|e| io::Error::new(ErrorKind::Other, e.to_string()))?;
+        self.index.flush()
+    }
+
+    pub fn write_entries<I>(&mut self, entries: I) -> io::Result<()>
+    where
+        I: IntoIterator<Item = Entry>,
+    {
+        for entry in entries {
+            self.write_entry(&entry)?;
+        }
+        Ok(())
+    }
+}
+
+pub struct LedgerReader {
+    offset: u64, // next start_offset
+    index: File,
+    data: File,
+}
+
+impl Iterator for LedgerReader {
     type Item = io::Result<Entry>;
 
     fn next(&mut self) -> Option<io::Result<Entry>> {
-        let mut entry_len_bytes = [0u8; sizeof(::<usize>()]; // TODO: sizeof()?
-        
-        let mut entry_len =
-            if self.reader.index
-            .read_exact(&mut entry_len_bytes[..self.entry_len_len])
-            .is_ok()
+        fn next_offset(file: &mut File) -> io::Result<u64> {
+            deserialize_from(file.take(size_of::<u64>() as u64))
+                .map_err(|e| io::Error::new(ErrorKind::Other, e.to_string()))
+        }
 
+        fn next_entry(file: &mut File, len: u64) -> io::Result<Entry> {
+            deserialize_from(file.take(len))
+                .map_err(|e| io::Error::new(ErrorKind::Other, e.to_string()))
+        }
+        match next_offset(&mut self.index) {
+            Ok(end_offset) => {
+                let len = end_offset - self.offset;
+                self.offset = end_offset;
+                Some(next_entry(&mut self.data, len))
+            }
+            Err(_) => None,
+        }
     }
 }
 
+/// Return an iterator for all the entries in the given file.
+pub fn read_ledger(directory: String) -> io::Result<impl Iterator<Item = io::Result<Entry>>> {
+    let directory = Path::new(&directory);
+
+    let index = File::open(directory.join("index"))?;
+    let data = File::open(directory.join("data"))?;
+
+    Ok(LedgerReader {
+        offset: 0,
+        index,
+        data,
+    })
+}
 
 // a Block is a slice of Entries
 pub trait Block {
@@ -204,6 +294,7 @@ mod tests {
     use hash::hash;
     use packet::{BlobRecycler, BLOB_DATA_SIZE, PACKET_DATA_SIZE};
     use signature::{KeyPair, KeyPairUtil};
+    use std;
     use std::net::{IpAddr, Ipv4Addr, SocketAddr};
     use transaction::{Transaction, Vote};
 
@@ -221,8 +312,7 @@ mod tests {
         assert!(!bad_ticks.verify(&zero)); // inductive step, bad
     }
 
-    #[test]
-    fn test_entries_to_blobs() {
+    fn make_test_entries() -> Vec<Entry> {
         let zero = Hash::default();
         let one = hash(&zero);
         let keypair = KeyPair::new();
@@ -248,7 +338,13 @@ mod tests {
         //                                V
         let mut transactions = vec![tx0; 362];
         transactions.extend(vec![tx1; 100]);
-        let entries = next_entries(&zero, 0, transactions);
+        next_entries(&zero, 0, transactions);
+    }
+
+    #[test]
+    fn test_entries_to_blobs() {
+        let entries = make_test_entries();
+
         let blob_recycler = BlobRecycler::default();
         let mut blob_q = VecDeque::new();
         entries.to_blobs(&blob_recycler, &mut blob_q);
@@ -316,17 +412,46 @@ mod tests {
         assert!(entries0[0].has_more);
         assert!(!entries0[entries0.len() - 1].has_more);
         assert!(entries0.verify(&id));
-        // test hand-construction... brittle, changes if split method changes... ?
-        //        let mut entries1 = vec![];
-        //        entries1.push(Entry::new(&id, 1, transactions[..threshold].to_vec(), true));
-        //        id = entries1[0].id;
-        //        entries1.push(Entry::new(
-        //            &id,
-        //            1,
-        //            transactions[threshold..].to_vec(),
-        //            false,
-        //        ));
-        //
-        //        assert_eq!(entries0, entries1);
     }
+
+    #[test]
+    fn test_ledger_reader_writer() {
+        let keypair = KeyPair::new();
+
+        let ledger_path = {
+            let id = {
+                let ids: Vec<_> = keypair
+                    .pubkey()
+                    .iter()
+                    .map(|id| format!("{}", id))
+                    .collect();
+                ids.join("")
+            };
+
+            format!("target/test_ledger_reader_writer_window-{}", id)
+        };
+
+        let entries = make_test_entries();
+
+        let mut writer = LedgerWriter::new(ledger_path.clone()).unwrap();
+        writer.write_entries(entries.clone()).unwrap();
+
+        let mut read_entries = vec![];
+        for x in read_ledger(ledger_path.clone()).unwrap() {
+            let entry = x.unwrap();
+            trace!("entry... {:?}", entry);
+            read_entries.push(entry);
+        }
+        assert_eq!(read_entries, entries);
+
+        let mut window = LedgerWindow::new(ledger_path.clone()).unwrap();
+
+        for (i, entry) in entries.iter().enumerate() {
+            let read_entry = window.get_entry(i as u64).unwrap();
+            assert_eq!(*entry, read_entry);
+        }
+
+        std::fs::remove_dir_all(ledger_path).unwrap();
+    }
+
 }