diff --git a/README.md b/README.md
new file mode 100644
index 0000000..b1b69ae
--- /dev/null
+++ b/README.md
@@ -0,0 +1,44 @@
+# FusionCalculator
+The calculator written in [Fusion language](https://github.com/fusionlanguage/fut). Can be translated to C and C#. Can be compiled as executable or library.
+
+### Building
+Requirements: fut, bash, dotnet8 (for c#), gcc (for C)
+
+Just generate C# source files:
+```shell
+./build_cs.sh --translate-only
+```
+Build C# executable:
+```shell
+./build_cs.sh
+```
+Build C executable:
+```shell
+./build_c.sh
+```
+Build C executable with debug symbols:
+```shell
+./build_c.sh --debug
+```
+
+## Executable usage
+Just call exe file in bin/ with math expression arguments:
+```shell
+bin/FusionCalculator.exe 1+2
+3
+bin/FusionCalculator.exe '11/(99-88)'
+1
+bin/FusionCalculator.exe '-1+6*(-2)'
+-13
+```
+
+## Library usage
+The public interface is very simple:
+```cs
+namespace FusionCalculator {
+  public static class Calculator {
+    public static double Calculate(string);
+  }
+}
+```
+Just call Calculate and get the result!