Lakes are time capsules. On Earth, they are considered sentinels of climate change and may have played the same role on early Mars. Their basins capture the record of geological and environmental fluctuations over a wide range of temporal and spatial scales. Terrestrial lakes host a diversity of habitats where life’s adaptability can be pushed to the edge in often unstable environments. They preserve the evidence of ancient life as sedimentation rapidly entombs dead organisms and generates anoxic conditions favoring the formation of fossils. This makes them prime candidates for exploration. The existence of lakes on ancient Mars is now widely accepted but that was not always the case. The history of science shows that knowledge on any scientific question is shaped by the means of exploration and those means are molded by what we think the world is. Prior to Mars Global Surveyor, the relatively low resolution of orbital imagery made it difficult to confirm Martian paleolakes by direct observations, though their existence was inferred because valley networks had already been identified on Viking and Mariner 9 images. Interpretation rested on ambiguous morphological evidence at 200 m/pixel on average with only localized coverage at higher resolution. Today, high-resolution imagery, morphology, geology, and mineralogy converge to support the existence of ancient standing bodies of water on Mars. This evidence is collectively examined by 33 authors and co-authors in the first monograph on the subject entitled /Lakes on Mars/, a book to be published by Elsevier, September 3, 2010 (Nathalie A. Cabrol and Edmond A. Grin, Eds). Here, Dr. Nathalie Cabrol will discuss the evidence presented in the book, its environmental significance in terms of climate and habitability, and the questions it still raises.