We present an algorithm for detecting the location of cells from two-photon calcium imaging data. In our 1 framework, multiple coupled active contours evolve, guided by a model-based cost function, to identify cell 2 boundaries. An active contour seeks to partition a local region into two subregions, a cell interior and ex-3 terior, in which all pixels have maximally 'similar' time courses. This simple, local model allows contours to 4 be evolved predominantly independently. When contours are sufficiently close, their evolution is coupled, 5 in a manner that permits overlap. We illustrate the ability of the proposed method to demix overlapping 6 cells on real data. The proposed framework is flexible, incorporating no prior information regarding a cell's 7 morphology or stereotypical temporal activity, which enables the detection of cells with diverse properties. 8 We demonstrate algorithm performance on a challenging mouse in vitro dataset, containing synchronously 9 spiking cells, and a manually labelled mouse in vivo dataset, on which ABLE achieves a 67.5% success 10 rate. We developed a versatile algorithm based on a popular image segmentation approach (the Level Set 18 Method) and demonstrated its capability to overcome these challenges. We include no assumptions on 19 cell shape or stereotypical temporal activity. This lends our framework the flexibility to be applied to new 20 datasets with minimal adjustment.