Phase diagram mapping is a useful method for predicting and rationalizing unusual thermally and mechanically triggered crystal transition phenomena. Here we focus on crystals of pimelic acid, which is known to exist as at least three polymorphs: modifications I–III. Modification III exhibits twinning ferroelasticity and a polymorphic transition, involving superelastic behavior by shearing. Additionally, a phase transition from modification III to modification II by heating involves a rapid expansion of crystals. The reverse transition from the metastable modification II to the thermally stable modification III at ambient temperature by mechanical stimuli involves rapid shrinkage, causing crystals to jump or rapidly fragment. For the first time a comprehensive phase diagram has been presented that accounts for the three different mechanical responses observed for pimelic acid: jumping/fragmentation, superelasticity, and ferroelasticity. Both thermal and mechanical transitions have been rationally mapped on the phase diagram.