SNCTRL is an optimal control interface for the software package SNOPT, written in Fortran 2003 and built and tested on version 7.5-2 of SNOPT. The optimal control problems are solved by discretizing and transforming the problem into a finite-dimensional nonlinear program (NLP). Several methods exist for discretizing the problem including single shooting, multiple shooting and collocation; SNCTRL implements a collocation method. Once the problem has been discretized, SNCTRL sets up the NLP and the required data structures for SNOPT.