This project is to investigate the dynamics of large populations of coupled nonlinear oscillators. Such systems provide simplified models of biological oscillator networks that occur in the heart, pancreas, intestine and brain. Oscillator populations are also used to model charge-density wave systems in solid-state physics. Included in this study are questions about synchronized clusters in oscillator lattices, enhancement of precision of noisy oscillators through mutual coupling, genericity of phase models with antisymmetric coupling, and collective behavior of systems of lambda-omega oscillators with random pinning and distributed frequencies. This work will continue and extend previous studies of the collective dynamics of oscillator populations.