Amorphous silicon a-Si:H thin film transistors (TFTs) are the dominant devices for high quality, large area active matrix liquid crystal displays (AM-LCDs) today. Although many thin film technologies used in the fabrication of a-Si:H TFTs are similar to those used in very large scale integrated circuits, they are different in their structures, materials, and device requirements. In this paper, the author reviews two of the most critical plasma technologies, plasma etching (PE)/reactive ion etching (RIE) and plasma-enhanced chemical vapor deposition (PECVD), in preparing a-Si:H TFTs according to above categories. Examples in each subject are given and discussed. Key factors in this paper are the plasma process effects on TFT performance. A summary on the short- and long-term research and development needs in these fields is included at the end.