An oscillator assembly which, in one embodiment, is an ovenized crystal oscillator assembly including an enclosure defined by a base and a lid which is seated on the base. The components of the oscillator assembly are supported by the base and located under the lid. The base and the lid together define an interior oven and are both preferably made of an insulative thermoplastic material to maximize the heat retention and oven performance of the oscillator assembly. In one embodiment, the lid and the base incorporate a clip for securing the lid to the base.