Write once run anywhere is both a blessing and a curse. For years, the WORA promise has ensured a consistent, compile-free experience for JVM users. Unfortunately, sometimes pure-Java libraries just can't do what developers need done. Sometimes, you just have to go full native. The Java Native Runtime is a core library and suite of support libraries for binding and calling out to native code. Without writing a line of C, you can make native calls, pass callbacks, and manage off-heap memory; every OS, library, and kernel-level feature is available to Java developers. I'll show how JNR is designed, compare code and performance with alternative approaches, and talk about why the JDK needs a standard FFI (foreign function interface) in Java 9.