diff --git a/CHANGELOG.md b/CHANGELOG.md
index 09c46c8..d4789d6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,9 @@ Changelog
 * Added an implementation of the `allocate()` function from Fowler's
   Enterprise Design Patterns.
 * Fixed parsing string numbers without a fractional part.
+* Added `toSource()` and `fromSource()` methods to easily get access to the
+  underlying bigint.
+* `Money.value` is now private.
 
 
 0.2.0 (2018-12-12)
diff --git a/readme.md b/readme.md
index d543825..fc8d319 100644
--- a/readme.md
+++ b/readme.md
@@ -162,12 +162,6 @@ number of digits you are interested in.
 For USD and most currencies this is 2. It's required to pass this argument
 because the Money object can't guess the desired precision.
 
-### TODO
-
-1. toSource (to get the underlying bigint value)
-2. fromSource (to create a new Money object from a high-precision
-   bigint value)
-
 
 Why is this library needed?
 ---------------------------
diff --git a/src/money.ts b/src/money.ts
index 013e989..6a8cba7 100644
--- a/src/money.ts
+++ b/src/money.ts
@@ -10,7 +10,7 @@ import {
 export class Money {
 
   currency: string;
-  value: bigint;
+  private value: bigint;
 
   constructor(value: number | bigint | string, currency: string) {
 
@@ -40,8 +40,7 @@ export class Money {
     }
 
     const addVal = moneyValueToBigInt(val);
-    const r = new Money(0, this.currency);
-    r.value = addVal + this.value;
+    const r = Money.fromSource(addVal + this.value, this.currency);
     return r;
 
   }
@@ -53,9 +52,7 @@ export class Money {
     }
 
     const subVal = moneyValueToBigInt(val);
-    const r = new Money(0, this.currency);
-    r.value = this.value - subVal;
-    return r;
+    return Money.fromSource(this.value - subVal, this.currency);
 
   }
 
@@ -75,9 +72,10 @@ export class Money {
     // Converting the dividor.
     const val2 = moneyValueToBigInt(val);
 
-    const result = new Money(0, this.currency);
-    result.value = nearestEvenDivide(val1, val2);
-    return result;
+    return Money.fromSource(
+      nearestEvenDivide(val1, val2),
+      this.currency
+    );
 
   }
 
@@ -91,9 +89,10 @@ export class Money {
     // Converting the dividor.
     const resultBig = valBig * this.value;
 
-    const result = new Money(0, this.currency);
-    result.value = nearestEvenDivide(resultBig, PRECISION_M);
-    return result;
+    return Money.fromSource(
+      nearestEvenDivide(resultBig, PRECISION_M),
+      this.currency
+    );
 
 
   }
@@ -163,12 +162,38 @@ export class Money {
 
     return result.map( item => {
 
-      const m = new Money(0, this.currency);
-      m.value = item * precisionRounder;
-      return m;
+      return Money.fromSource(
+        item * precisionRounder,
+        this.currency
+      );
 
     });
 
   }
 
+  /**
+   * Returns the underlying bigint value.
+   *
+   * This is the current value of the object, multiplied by 10 ** 12.
+   */
+  toSource(): bigint {
+
+    return this.value;
+
+  }
+
+  /**
+   * A factory function to construct a Money object a 'source' value.
+   *
+   * The source value is just the underlying bigint used in the Money
+   * class and can be obtained by calling Money.getSource().
+   */
+  static fromSource(val: bigint, currency: string): Money {
+
+    const m = new Money(0, currency);
+    m.value = val;
+
+    return m;
+
+  }
 }
diff --git a/src/util.ts b/src/util.ts
index c4f88c4..c0ab00a 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -19,7 +19,7 @@ export const PRECISION_M = 10n ** PRECISION;
 export function moneyValueToBigInt(input: Money | string | number | bigint): bigint {
 
   if (input instanceof Money) {
-    return input.value;
+    return input.toSource();
   }
 
   switch (typeof input) {
diff --git a/test/money.ts b/test/money.ts
index 1c6dbab..3043b9f 100644
--- a/test/money.ts
+++ b/test/money.ts
@@ -317,11 +317,22 @@ describe('Money class', () => {
         expect(result.map( item => item.toFixed(cas[2]))).to.eql(cas[3]);
 
         // Double-check. Numbers must exactly add up to the source value
-        expect(result.reduce( (acc, cur) => acc + cur.value, 0n)).to.equal(x.value);
+        expect(result.reduce( (acc, cur) => acc + cur.toSource(), 0n)).to.equal(x.toSource());
 
       });
 
     }
   });
 
+  describe('toSource', () => {
+
+    it('should return the underlying source bigint value', () => {
+
+      const m = new Money(1, 'USD');
+      expect(m.toSource()).to.equal(1000000000000n);
+
+    });
+
+  });
+
 });