Cells are able to generate phenotypic diversity both during development and in response to stressful and changing environments, aiding survival. The biologically and medically vital process of a cell assuming a functionally important fate from a range of phenotypic possibilities can be thought of as a cell decision. To make these decisions, a cell relies on energy dependent pathways of signalling and expression. However, energy availability is often overlooked as a modulator of cellular decisionmaking. As cells can vary dramatically in energy availability, this limits our knowledge of how this key biological axis affects cell behaviour. Here, we consider the energy dependence of a highly generalisable decision-making regulatory network, and show that energy variability changes the sets of decisions a cell can make and the ease with which they can be made. Increasing intracellular energy levels can increase the number of stable phenotypes it can generate, corresponding to increased decision-making capacity. For this decision-making architecture, a cell with intracellular energy below a threshold is limited to a singular phenotype, potentially forcing the adoption of a specific cell fate. We suggest that common energetic differences between cells may explain some of the observed variability in cellular decision-making, and demonstrate the importance of considering energy levels in several diverse biological decision-making phenomena. endospores is a survival mechanism used by diverse genera including Bacillus and Clostridium 25 , contributing to foodborne disease and food spoilage 26,27 . The decision to become a persister cell (a phenotype more tolerant to external stress, including antibiotics), is made in several bacterial species 28-31 and can have a dramatic impact on the efficacy of treatments [32][33][34][35] .Many of the mechanisms behind cellular decision-making in eukaryotes and prokaryotes remain poorly understood. Regulatory networks, representing the interactions between genes that govern these decisions, are often used to summarise our knowledge 36 . Typically, edges in a schematic network illustrate processes such as transcription and translation and nodes represent genes. However, this coarse-graining can often omit a substantial amount of important detail. In particular, the fact that the processes represented by these edges are energy dependent (Figure 1) is rarely considered. Transcription and translation require a substantial ATP budget 37, 38 , so there exists a core energy dependence in the dynamics of gene regulatory networks, potentially affecting the decisions supported by a given cell.This energy dependence is important because different cells, particularly in microbiology, can have substantially different levels of available energy. Energy variability has been observed within genetically-identical Escherichia coli bacteria cells in a population, where absolute concentrations of intracellular ATP were spread over at least half an order of magnitude, in a skewed distribution around 1.54 ± 1...