We present the GLoBES ("General Long Baseline Experiment Simulator") software package, which allows the simulation of long-baseline and reactor neutrino oscillation experiments. One part of the software is the abstract experiment definition language to define experiments with beam and full detector descriptions as accurately as possible. Many systematics options are provided, such as normalization and energy calibration errors, or the choice between spectral or total rate information. For the definition of experiments, a new transparent building block concept is introduced. In addition, an additional program provides the possibility to develop and test new experiment definitions quickly. Another part of GLoBES is the user's interface, which provides probability, rate, and Delta(x)(2) information for a given experiment or any combination of up to 32 experiments in C. Especially, the Delta(x)(2) functions allow a simulation with statistics only, systematics, correlations, and degeneracies. In particular, GLoBES can handle the full multi-parameter correlation among the oscillation parameters, external input, and matter density uncertainties. (c) 2005 Elsevier B.V. All rights reserved.