Queen wasps are the centre of a wasp nest, and the rest of the wasps in a colony exist to feed and care for her. She is the only female in a colony able to lay eggs, so the colony's survival depends upon her. Queen wasps look basically the same as worker wasps, making it difficult to identify them. However, some basic knowledge of the life cycle of a wasp gives you all the information you need to recognise a queen wasp when you see one.
Note the time of year. If it is early spring, any living wasp you see is a queen wasp -- queens are the only wasps that survive the autumn, and new worker wasps do not hatch from their eggs until later in the season.
Approach the wasp in question carefully and compare it to other wasps. Queen wasps and worker wasps look alike except for their size: queens are noticeably bigger. If you can see multiple wasps and one is clearly bigger than the others, she is the queen.
Identify a queen in the fall by looking for solitary wasps. The queen departs her nest at the end of the summer, so none of the insects remaining in a hive or swarm during the fall are the queen.
Identify a queen in the winter by finding a dormant wasp. The rest of the nest is dead, so any living wasp is a queen. She hibernates, or overwinters, in a small, dry space, such as inside a rotting tree trunk or under wooden trim in a house. If you see a solitary, overwintering wasp in the winter, it is a queen.