Abstract: Optical nonreciprocal devices, such as optical isolators, circulators and phase shifts, are basic units of all-optical communications and have important applications in optical signal processing and quantum networks. Standard approaches for optical nonreciprocity make use of magneto-optical properties (e.g. Faraday rotation), which however requires large magnetic fields, and thus makes it difficult for integration on a small scale. To overcome this problem, other magnetic-free approaches have been proposed. In this paper, we will introduce recent developments on magnetic-free optical nonreciprocity, and also our recent research on thermal motion induced optical nonreciprocity and unidirectional amplification.