Accretion disks are pivotal elements in the formation and earlyevolution of solar-like stars. On top of supplying the raw material,their internal conditions also regulate the formation of planets.Their study therefore holds the key to solve this long standingmystery: how did our Solar System form? This chapter focuses onobservational studies of the circumstellar environment, and inparticular of circumstellar disks, associated with pre-main sequencesolar-like stars. The direct measurement of disk parameters poses anobvious challenge: at the distance of the typical star forming regions( e.g. ~140 pc for Taurus), a planetary system like ours (withdiameter ≅50 AU out to Pluto, but excluding the Kuiper belt which could extend much farther out) subtends only 0.35''. Yetits surface brightness is low in comparison to the bright central starand high angular and high contrast imaging techniques are required ifone hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1'' resolution or betterand high contrast have been available for just about 10 yearsnow. They are covering a large part of the electromagnetic spectrum,from the UV/Optical with HST and the near-infrared from ground-basedadaptive optics systems, to the millimetric range with long-baselineradio interferometers. It is therefore not surprising that ourknowledge of the structure of the disks surrounding low-mass stars hasmade a gigantic leap forward in the last decade. In the following pages we will attempt to describe, in a historicalperpective, the road that led to the idea that most solar-like starsare surrounded by an accretion disk at one point in their early lifeand how, nowadays, their structural and physical parameters can beestimated from direct observations. We will follow by a shortdiscussion of a few of the constraints available regarding theevolution and dissipation of these disks. This last topic isparticularly relevant today to understand the mechanism leading to theformation of planets.