The question of animal language and thought has been debated since ancient times. Some have held the view that humans are exceptional in these respects, while others believe that humans and animals are similar with respect to language and thought. The issue is important because our self-image as a species is at stake. Arguments for human exceptionalism such as Cartesian, Wittgensteinian and behaviourist state that language and thought are closely associated, and animals do not have language. The ape language experiments of the 1960s and 1970s were especially important against this background: if apes could learn language then even the advocates of human exceptionalism would have to admit that they have thoughts. It is now generally believed that whatever linguistic abilities apes have shown have been quite rudimentary. Yet many sceptics are willing to grant that in some cases apes did develop linguistic skills to some extent, and clearly evidenced thought. Studies of other animals in captivity and various animals in the wild have provided evidence of highly sophisticated communicative behaviour. Cognitive ethology and comparative psychology have emerged as the fields that study animal thought. While there are conceptual difficulties in grounding these fields, it appears plausible that many animals have thoughts and these can be scientifically investigated.