diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..132c216
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+hll.iml
diff --git a/src/main/java/net/agkn/hll/HLL.java b/src/main/java/net/agkn/hll/HLL.java
index cdfd3ad..5f4fba0 100644
--- a/src/main/java/net/agkn/hll/HLL.java
+++ b/src/main/java/net/agkn/hll/HLL.java
@@ -16,6 +16,7 @@
  * limitations under the License.
  */
 
+import java.io.Serializable;
 import java.util.Arrays;
 
 import it.unimi.dsi.fastutil.ints.Int2ByteOpenHashMap;
@@ -59,7 +60,7 @@
  *
  * @author timon
  */
-public class HLL implements Cloneable {
+public class HLL implements Cloneable, Serializable {
     // minimum and maximum values for the log-base-2 of the number of registers
     // in the HLL
     public static final int MINIMUM_LOG2M_PARAM = 4;
@@ -75,6 +76,7 @@ public class HLL implements Cloneable {
     public static final int MINIMUM_EXPTHRESH_PARAM = -1;
     public static final int MAXIMUM_EXPTHRESH_PARAM = 18;
     public static final int MAXIMUM_EXPLICIT_THRESHOLD = (1 << (MAXIMUM_EXPTHRESH_PARAM - 1)/*per storage spec*/);
+    private static final long serialVersionUID = -848939697379806659L;
 
     // ************************************************************************
     // Storage
diff --git a/src/main/java/net/agkn/hll/HLLType.java b/src/main/java/net/agkn/hll/HLLType.java
index 61e3c79..9fdcede 100644
--- a/src/main/java/net/agkn/hll/HLLType.java
+++ b/src/main/java/net/agkn/hll/HLLType.java
@@ -16,11 +16,13 @@
  * limitations under the License.
  */
 
+import java.io.Serializable;
+
 /**
  * The types of algorithm/data structure that {@link HLL} can utilize. For more
  * information, see the Javadoc for {@link HLL}.
  */
-public enum HLLType {
+public enum HLLType implements Serializable {
     EMPTY,
     EXPLICIT,
     SPARSE,
diff --git a/src/main/java/net/agkn/hll/util/BitVector.java b/src/main/java/net/agkn/hll/util/BitVector.java
index 56687b1..df8ca84 100644
--- a/src/main/java/net/agkn/hll/util/BitVector.java
+++ b/src/main/java/net/agkn/hll/util/BitVector.java
@@ -18,6 +18,8 @@
 
 import net.agkn.hll.serialization.IWordSerializer;
 
+import java.io.Serializable;
+
 /**
  * A vector (array) of bits that is accessed in units ("registers") of <code>width</code>
  * bits which are stored as 64bit "words" (<code>long</code>s).  In this context
@@ -25,7 +27,7 @@
  *
  * @author rgrzywinski
  */
-public class BitVector implements Cloneable {
+public class BitVector implements Cloneable, Serializable {
     // NOTE:  in this context, a word is 64bits
 
     // rather than doing division to determine how a bit index fits into 64bit
@@ -40,6 +42,7 @@ public class BitVector implements Cloneable {
 
     // ========================================================================
     public static final int BYTES_PER_WORD = 8/*8 bytes in a long*/;
+    private static final long serialVersionUID = -2191980917150692709L;
 
     // ************************************************************************
     // 64bit words