  The type I ELMy H-mode is the baseline operating scenario for ITER. While it
is known that the type I ELM ultimately results from the peeling-ballooning
instability, there is growing experimental evidence that a mode grows up before
the ELM crash that may modify the edge plasma, which then leads to the ELM
event due to the peeling-ballooning mode. The triggered mode results in the
release of a large number of particles and energy from the core plasma but the
precise mechanism by which these losses occur is still not fully understood and
hence makes predictions for future devices uncertain. Our current understanding
of the processes that trigger type I ELMs and the size of the resultant energy
loss are reviewed and compared to experimental data and ideas for further
development are discussed.
