Immune specificity is usually described in terms of the lock-and-key metaphor. However, this metaphor is to a certain extent misleading and does not convey the complexity underlying immune specificity. The failure of the lock-and-key metaphor makes it difficult to understand immune specificity and recognition. This is the reason why immune specificity has been described as the specificity enigma. In this chapter, I point to three important differences between biological specificity and the mechanical specificity that underlies the lock-and-key metaphor. I further suggest an alternative lens through which immune specificity can be considered.