This paper presents language features for High PerformanceFortran HPF to specify non-local access patterns of distributed arrays, called halos, and to control the communication associated with these non-local accesses. Using these features crucial optimization techniques required for an e cient parallelization of irregular applications may b e applied. The information provided by halos is utilized by the compiler and runtime system to optimize the management of distributed arrays and the computation of communication schedules. High-level communication primitives for halos enable the programmer to avoid redundant communication, to reuse communication schedules, and to hide communication overheads by o verlapping communication with computation. Performance results of a kernel from a crash simulation code on the NEC Cenju-4, the IBM SP2, and on the NEC SX-4 show that by using the proposed extensions a performance close to hand-coded message-passing codes can be achieved for irregular problems.