Classical trabeculectomy is affected by numerous and serious drawbacks that have led to the development of nonpenetrating surgery. In this new filtering technique, the aqueous outflow through the juxtacanalicular trabeculum and Schlemm's canal is selectively increased without penetrating the anterior chamber. This is best performed by means of a careful and precise dissection of the outflow resistance pathway and by removing its most resistant portion. This requires both mastery of the microdissection technique and high-precision surgical tools. Finally, sound knowledge of the morphological features of such delicate structures is of paramount importance to avoid intra- and postoperative complications.