The need for efficient cell separation, an essential preparatory step in many biological and medical assays, has lead to the recent development of numerous microscale separation techniques. Developing efficient microscale separation methods that offer a greater control over cell population distribution are important for realizing true point-of-care (POC) lab-on-a-chip (LOC) systems. We have recently reviewed the current state-of-the-art in microfluidics based cell separation techniques (Ali Asgar S. Bhagat, Hansen Bow, Han Wei Hou, Swee Jin Tan, Jongyoon Han, Chwee Teck Lim, "Microfluidics for cell separation" - SPECIAL ISSUE - REVIEW, Medical and Biological Engineering & Computing, Published On-line, 23rd April 2010). Microfluidics based sorting offers numerous advantages: reduced sample volumes, faster sample processing, high sensitivity and spatial resolution, low device cost and increased portability. The techniques presented are broadly classified as being active or passive depending on the operating principles. Active techniques rely on an external force field for functionality, while passive techniques rely entirely on the channel geometry and inherent hydrodynamic forces for functionality. In lieu of this classification, this review compares various passive and active cell separation techniques developed on the microscale. The various separation principles are explained in detail along with popular examples demonstrating its application towards cell separation. Common separation metrics including separation markers, resolution, efficiency and throughput of these techniques are discussed.