Kant wrote extensively on all major topics of intellectual interest. In terms of the publication of major texts his most prolific period was 1781 to 1790. In the domains of epistemology and metaphysics he published the Critique of Pure Reason in 1781, with a second edition in 1787. In the domain of ethics he published the Groundwork of the Metaphysics of Morals in 1785 and the Critique of Practical Reason in 1788. In the domain of asthetics he presented his theory in 1790 in the form of the Critique of Judgment.As a form of shorthand the three Critiques are known as the First, Second, and Third, respectively.
In the first Critique Kant deals with how we come to understand our world; in the second Critique he deals with practical reason and how we act in our world; and in the third Critique he attempts to show a systematic connection between the first two. So, the first deals with how we think about our sensible world, the second deals with how we act in it, and the third supplies a link between the two in terms of felt judgement. In the first he draws together our inner experience with our necessary perception of an external world. He combines perception and understanding through the application of the productive imagination in such a way as to make judgements possible. He links the First and the Third Critiques by arguing that aesthetic judgments, that is, judgements about what is beautiful or sublime, derive from our determination to impose order on our sensory experience. Thus, aesthetics is just like mathematics: it attempts to find unity in experience.
So, each of the Critiques is concerned with judgement, judgements of reason, moral judgements, and aesthetic judgements.