Inductive thinking is a vast topic, which connects with several areas normally considered to be outside the psychology of thinking, such as learning, problem solving, semantic memory, and psycholinguistics. Within the field of thinking, there are relations with deduction and scientific reasoning and with their associated theories, which we have considered in preceding chapters; and also with judgement and decision making, which we shall come to. Probably the most extensively researched area of induction within the psychology of thinking is that concerned with judgements of frequency and probability: the next chapter is devoted to that subject. In this one, we shall consider some other important aspects: generalisation, specialisation, categorisation, analogical thinking, and two types of theory: rule-based and model-based. There is no single normative theory for induction in general, although there is for that part of it concerned with probability judgement, as we shall see; thus we shall be less concerned in this chapter with the comparison between normative standards and human performance. Most of the relevant theoretical proposals about induction have come from psychology or artificial intelligence.