In this review, we address the relationship between stomatal behaviour, water potential regulation and hydraulic transport in plants, focusing on the implications for the iso/anisohydric classification of plant drought responses at seasonal timescales. We first revise the history of the isohydric concept and its possible definitions. Then, we use published data to answer two main questions: (1) is greater stomatal control in response to decreasing water availability associated with a tighter regulation of leaf water potential (ΨL) across species? and (2) is there an association between tighter ΨL regulation (~isohydric behaviour) and lower leaf conductance over time during a drought event? These two questions are addressed at two levels: across species growing in different sites and comparing only species coexisting at a given site. Our analyses show that, across species, a tight regulation of ΨL is not necessarily associated with greater stomatal control or with more constrained assimilation during drought. Therefore, iso/anisohydry defined in terms of ΨL regulation cannot be used as an indicator of a specific mechanism of drought‐induced mortality or as a proxy for overall plant vulnerability to drought. The relationship between leaf water potential regulation (iso/anisohydry) and stomatal behaviour is one of the foundations of our current understanding of plant water relations and drought responses. There are reasons, however, to expect that water potential regulation and stomatal behaviour may be (at least partially) uncoupled across species. We review the literature and provide a quantitative synthesis showing that species with a tight regulation of leaf water potential do not necessarily show greater stomatal control or more constrained assimilation during drought. Therefore, iso/anisohydry cannot be used as an indicator of a specific mechanism of drought‐induced mortality or as a proxy for overall plant vulnerability to drought.