The development of the Grid has opened new possibilities for scientists and engineers to execute large-scale modeling experiments. This has stimulated the generation and development of tools for the creation and management of complex computing experiments in the Grid. Among these, tools for the automation of the programming of experiments play a significant role. In this paper we present GriCoL, which we propose as a simple and efficient language for the description of complex Grid experiments. We also describe the environment within which GriCoL works, namely the Science Experimental Grid Laboratory (SEGL) system for designing and executing complex experiments. As an illustration, the paper includes the description of a biochemical experiment using Molecular Dynamics simulations.