Presented is a treecode implemented in C++ for the computation of long range interactions. This treecode is applied to three dimensional systems containing large numbers of particles. Although the approach is applicable to more general kernel functions, the kernel functions considered here are of the form, r-alpha, for alpha<3, where r is the distance between two particles. The direct implementation for computing the pairwise interactions, for a system of n particles, results in O(n2) operations, which is prohibitively expensive for large systems. The presented treecode reduces the cost to O(n log n) . Furthermore, the treecode is parallelized using MPI, which further reduces the cost to O(n log n / p), where P is the number of MPI processes.