Lisbon has a great selection of public/street art. There are also lots of tour on offer that would take you around and lead you to fantastic pieces around the city. 

I spotted the first piece in Alfahma during the Lisbon Photography Tour I took. Just walking around that area was full of little (and big) colourful surprises. Most Street Art walking tour go around that area. In attempt to spread tourists around the city of Lisbon, Graffiti artists collaborated to paint across the city. To properly see them all, you would need a car. 

We didn't have a car, so we started by going to the Under-Dog Art Store, which is located inside the Montana Lisboa Art Store (Address: Rua da Cintura do Porto, armazém A, nº 20 Cais do Sodré, Lisboa). The Underdog section of the store has a big map that shows you where the major pieces of art are located. You can also purchase a paper map -for €1.50- with the main spots and locations. We didn't have a lot of time, so we went to the Hall of Fame, which had lots of major art that was completed in a previous event. It was basically a very long circular wall (photos below). We also found a few other pieces by chance and walking around. 

You can also arrange a tour with the Under-Dog Art Store, but that needs a minimum of three days notice!