Overview: Stem cells are traditionally co-cultured with “feeder” cells (usually fibroblasts) derived from mouse or human. The feeder cells provide secreted factors, extracellular matrix, and cellular contacts for the maintenance of stem cells in the undifferentiated state without losing pluripotency. However feeder cells may poses a risk of cross-contamination such as passing animal pathogens to human embryonic stem (hES) cells hindering clinical application of hES cells. Feeder-free stem cell culture is a system for maintaining stem cells in the undifferentiated state without the need for direct contact with feeder cells. The medium for feeder-free stem cell culture is either conditioned by contact with mouse or human feeder cells, so called conditioned medium (CM), or supplemented with different growth factors and other signal transduction factors.