Filtering surgery is an effective and a most commonly used technique in managing glaucoma. However, the failure of surgery is often caused by the scar formation of the filtering pathway. It is important for clinicians to evaluate the morphology and the function of the filtering bleb, especially in the early period of post-operation when IOP is normal. The success of surgery relies upon the early intervention whenever the filtering bleb showing the tendency of scarring. This paper reviews recent development in the observation and the treatment of glaucoma filtering blebs.