We present an efficient and dynamic approach for calling native functions from within Java. Traditionally, programmers use the Java Native Interface (JNI) to call such functions. This paper introduces a new mechanism which we tailored specifically towards calling native functions from Java. We call it the Graal Native Function Interface (GNFI). It is faster than JNI in all relevant cases and more flexible because it avoids the JNI boiler-plate code.GNFI enables the user to directly invoke native code from Java applications. We describe how GNFI creates call stubs for native functions that a just-in-time (JIT) compiler can optimize and how we embed these stubs into Java code. We introduce different approaches for calling native functions from within compiled and interpreted Java code. In particular, we describe how our approach embeds the call stubs into a Java application so that the JIT-compiled code consists of a direct call to a native function.We evaluate the call overhead of GNFI. The measurements demonstrate a significant performance advantage of GNFI compared to JNI and the Java Native Access (JNA). Also, we evaluate our approach against JNI and JNA on a jblas matrix multiplication benchmark. The evaluation shows that GNFI outperforms JNI and JNA in compiled and interpreted mode by a factor of 1.9 in the best case.