The continuous-time filter field prior to using transconductance amplifiers as active devices will be reviewed. Motivation for using transconductance amplifiers (alternately Operational Transconductance Amplifiers) in the design of continuous-time filters in general and in integrated continuous-time filters in particular will be discussed. Challenges facing the transconductance-based filter research community in early 80’s will be reviewed. Unique performance capabilities offered by the transconductance amplifier will be identified. Key contributions of Edgar Sanchez in the design of OTAs and in their utilization in the analog circuits field will be highlighted.