The definition of a limit of a function is, without a doubt, one of the most fundamental and important concepts in Calculus. This site allows the user to visually explore the rigorous “epsilon-delta” definition of function limit that is typically introduced in the very beginning of the first semester of Calculus. Given a function, the user has control (via a slider) over delta parameter to choose a value of delta that is small enough to accommodate a generated value of epsilon. Also, there are two fields where the user can enter the actual limit value and the numeric value of delta based on the observation. These answers can be checked by pressing a button. Several exploration questions are also offered.