Infrared search and track (IRST) system is a wide field of view surveillance system, meant for autonomous search, detection, acquisition, and cue of potential targets. The first and second generation IRSTs utilized detectors with multiple elements followed by discrete preamplifiers for signal read-out. They have many performance limitations. With the advent of infrared focal plane array (IRFPA) sensors, the present trend is to build IRSTs based on line FPA sensors to achieve higher sensitivity and resolution. However, due to system limitations of line IRFPA sensors, scanning mode of IRST cannot be stopped at any desired position to scan a small sector of interest. They also suffer from more false alarms in target detection. In future, it may be desirable to reduce false alarms, and also to use an IRST system for closed-loop- tracking of a potential target, in addition to its surveillance mode. IRST based on area array sensors may be a better option for this purpose, but it may pose some problems when used in a surveillance mode. This paper addresses this issue. Design considerations of all sub-systems of an IRST based on line/area array sensors, such as scanner assembly, interface electronics with the sensor, nonuniformity correction, signal processor, and the display methodology to cover 360 degrees are also discussed.