diff --git a/ClosedXML/ClosedXML/ClosedXML/ClosedXML.csproj b/ClosedXML/ClosedXML/ClosedXML/ClosedXML.csproj
index 7f22e1d..4012c76 100644
--- a/ClosedXML/ClosedXML/ClosedXML/ClosedXML.csproj
+++ b/ClosedXML/ClosedXML/ClosedXML/ClosedXML.csproj
@@ -135,6 +135,7 @@
   <ItemGroup>
     <Compile Include="Excel\CalcEngine\Functions\DateAndTime.cs" />
     <Compile Include="Excel\CalcEngine\Functions\Database.cs" />
+    <Compile Include="Excel\CalcEngine\Functions\Is.cs" />
     <Compile Include="Excel\Misc\XLCallbackAction.cs" />
     <Compile Include="Excel\Misc\XLReentrantEnumerableSet.cs" />
     <Compile Include="Excel\XLConstants.cs" />
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/CalcEngine.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/CalcEngine.cs
index 7d93111..f646ddc 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/CalcEngine.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/CalcEngine.cs
@@ -285,6 +285,7 @@
                 _fnTbl = new Dictionary<string, FunctionDefinition>(StringComparer.InvariantCultureIgnoreCase);
 
                 // register built-in functions (and constants)
+                Is.Register(this);
                 Logical.Register(this);
                 MathTrig.Register(this);
                 Text.Register(this);
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/Is.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/Is.cs
new file mode 100644
index 0000000..544f92e
--- /dev/null
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/Is.cs
@@ -0,0 +1,21 @@
+using System;
+using System.Diagnostics;
+using System.Collections.Generic;
+using System.Text;
+
+namespace ClosedXML.Excel.CalcEngine
+{
+    internal static class Is
+    {
+        public static void Register(CalcEngine ce)
+        {
+            ce.RegisterFunction("ISBLANK", 1, IsBlank);
+        }
+
+        static object IsBlank(List<Expression> p)
+        {
+            var v = (string)p[0];
+            return String.IsNullOrEmpty(v);
+        }
+    }
+}
diff --git a/ClosedXML/ClosedXML/ClosedXML_Net3.5/ClosedXML_Net3.5.csproj b/ClosedXML/ClosedXML/ClosedXML_Net3.5/ClosedXML_Net3.5.csproj
index b41afcb..f057b4d 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Net3.5/ClosedXML_Net3.5.csproj
+++ b/ClosedXML/ClosedXML/ClosedXML_Net3.5/ClosedXML_Net3.5.csproj
@@ -180,6 +180,9 @@
     <Compile Include="..\ClosedXML\Excel\CalcEngine\Functions\DateAndTime.cs">
       <Link>Excel\CalcEngine\Functions\DateAndTime.cs</Link>
     </Compile>
+    <Compile Include="..\ClosedXML\Excel\CalcEngine\Functions\Is.cs">
+      <Link>Excel\CalcEngine\Functions\Is.cs</Link>
+    </Compile>
     <Compile Include="..\ClosedXML\Excel\CalcEngine\Functions\Logical.cs">
       <Link>Excel\CalcEngine\Functions\Logical.cs</Link>
     </Compile>
diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/ClosedXML_Tests.csproj b/ClosedXML/ClosedXML/ClosedXML_Tests/ClosedXML_Tests.csproj
index 2e26442..dbc5325 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/ClosedXML_Tests.csproj
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/ClosedXML_Tests.csproj
@@ -114,6 +114,7 @@
     <Compile Include="Examples\RowsTests.cs" />
     <Compile Include="Examples\StylesTests.cs" />
     <Compile Include="ExcelDocsComparerTests.cs" />
+    <Compile Include="Excel\CalcEngine\IsTests.cs" />
     <Compile Include="Excel\CalcEngine\LogicalTests.cs" />
     <Compile Include="Excel\CalcEngine\TextTests.cs" />
     <Compile Include="XLHelperTests.cs" />
diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/IsTests.cs b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/IsTests.cs
new file mode 100644
index 0000000..2d98c68
--- /dev/null
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/IsTests.cs
@@ -0,0 +1,28 @@
+using System;
+using ClosedXML.Excel;
+using NUnit.Framework;
+
+namespace ClosedXML_Tests.Excel.CalcEngine
+{
+
+    [TestFixture]
+    public class IsTests
+    {
+        [Test]
+        public void IsBlank_true()
+        {
+            var ws = new XLWorkbook().AddWorksheet("Sheet");
+            var actual = ws.Evaluate("=IsBlank(A1)");
+            Assert.AreEqual(true, actual);
+        }
+
+        [Test]
+        public void IsBlank_false()
+        {
+            var ws = new XLWorkbook().AddWorksheet("Sheet");
+            ws.Cell("A1").Value = " ";
+            var actual = ws.Evaluate("=IsBlank(A1)");
+            Assert.AreEqual(false, actual);
+        }
+    }
+}
\ No newline at end of file