Perhaps the most important aspect of setting up your aquarium is the initial planning and preparation. Mishaps or failure at this stage of the process are very hard to correct later on. It is, therefore, important that you read about the subject, visit well-run public aquariums, join aquarium societies, and speak with experienced aquarists whenever possible. In this chapter, we will examine the important considerations necessary for success in establishing a freshwater or marine aquarium. Although not absolutely necessary, experience with freshwater aquariums will prove very useful for those seeking to keep marine aquariums.