Oscillatory activities are hallmarks of brain output that are linked to normal and pathological functioning. Thus, determining mechanisms for how brain oscillations are generated is essential. However, the multi-scale, nonlinear nature of our brains makes them highly challenging to understand. In particular, theta oscillations (3-12 Hz) were discovered almost 80 years ago and are one of the most robust oscillations in the brain, including the hippocampus where they are associated with exploration. Although several cellular-based network models of varying levels of complexity have been developed, it is still unclear how theta oscillations are generated in the hippocampus. In this talk, I will describe the development of our cellular-based network models where we have taken advantage of an *in vitro* whole hippocampus preparation that spontaneously generates theta rhythms. Using theoretical insights and biological constraints, our developed models can produce theta rhythms, thus suggesting the underlying essence of their generation.