The time evolution of Edge Localized Modes (ELMs) in the JET tokamak is investigated using the JETTO predictive modeling code. It is found that both pressure-driven ballooning and current-driven peeling modes can play a role in triggering the ELM crashes. In the simulations carried out, each large ELM consists of a sequence of quasi-continuous small ELM crashes. Each sequence of ELM crashes is separated from the next sequence by a relatively longer ELMfree period. The initial crash in each ELM sequence can be triggered either by a pressure-driven ballooning mode or by a current-driven peeling mode, while the subsequent crashes within that sequence are triggered by current-driven peeling modes, which are made more unstable by the reduction in the pressure gradient resulting from the initial crash. The HELENA and MISHKA ideal MHD stability codes are used to validate the stability criteria used in the JETTO simulations. This stability analysis includes infinite-n ideal ballooning, finite-n ballooning, and low-n kink/peeling modes. The simulations and the associated stability analysis may lead to an improved understanding of the physical mechanisms that control the evolution of ELMs.