In 1999, Alÿs' first solo exhibition at Lisson Gallery was opened to the public featuring his Sleepers series. Focusing primarily on Mexico City, such images can be seen as extensions of his walking around documenting Mexico City in its crude daily life and its struggle to resist and survive modernity. Although no longer represented by the gallery, Alÿs work was included in the 2016 group show Performer/Audience/Mirror an exhibition which spanned the work of Lisson artists from the 1960s to the present day. 

"In his series of slides of stray dogs and homeless street dwellers (Sleepers, 1999 – 2001) Alÿs keeps literally to this ground-level perspective, avoiding sharp angles and voyeuristic close-ups. With this formal show of respect he prevents the portraits from becoming patronising demonstrations of pity. Taking a nap in doorways, on benches or on the sunlit pavement, the protagonists become strangely noble, sleeping the sleep of the just. For a brief moment the equation of dogs with humans seems like an antidote to the trope of humans being treated like dogs."
- Jörg Heiser, ‘Walk on the Wild Side’, Frieze, September 2002