A plaintiff may establish Art. III standing for purposes of bringing a suit for discrimination against the disabled under the federal ADA by showing that he had actual knowledge of the defendant’s violations of the ADA by failure to make suitable accommodations for disabled persons, and that he was deterred from using defendant’s facilities as a result of that knowledge. It does not matter that plaintiff did not actually visit the facilities and witness the barriers for disabled persons so long as he knows they exist. It also does not matter what plaintiff’s motivation was, so the fact he was a “tester” does not deprive him of standing. However, the decision also affirms denial of class certification since the defendant is a REIT that must and does hire third parties to manage its properties, and those third parties’ policies differ. This defeats commonality even if the REIT is liable for its agents’ ADA violations.