The spatiotemporal bioelectrical signals produced by living bodies play a significant role in enlightening biological functions. In recent years, flexible devices have emerged as a means of monitoring biological information. In order to measure bioelectrical signals using a two-dimensional flexible device, it is necessary to combine a flexible multielectrode array with an active matrix that minimizes the number of wires. It is necessary for the flexible active multielectrode array to possess several attributes based on its application, including high spatiotemporal resolution, conformability, flexibility, transparency, and biocompatibility. Applications may include long-term health monitoring, disease detection, and optogenetic observation tools for long-term recording. This work describes devices that possess the attributes mentioned above. The first part of this work describes a flexible active multielectrode array which implements conformability. The second part discusses a transparent active multielectrode array used to receive optical-spatial information with bioelectric signals. Third, a biocompatible flexible active multielectrode array is described. Finally, future prospects for flexible active multielectrode arrays are discussed from the perspective of materials science and electronic engineering.