Title: An Experiment Design Paradigm using Joint Feature Selection and Task Optimization. Abstract: This paper presents a subsampling-task paradigm for data-driven task-specific experiment design (ED) and a novel method in populationwide supervised feature selection (FS).  Optimal ED, the choice of sampling points under constraints of limited acquisition-time, arises in a wide variety of scientific and engineering contexts. However the continuous optimization used in classical approaches depend on a-priori parameter choices and challenging non-convex optimization landscapes.  This paper proposes to replace this strategy with a subsampling-task paradigm, analogous to populationwide supervised FS.  In particular, we introduce JOFSTO, which performs JOint Feature Selection and Task Optimization.  JOFSTO jointly optimizes two coupled networks: one for feature scoring, which provides the ED, the other for execution of a downstream task or process.  Unlike most FS problems, e.g. selecting protein expressions for classification, ED problems typically select from highly correlated globally informative candidates rather than seeking a small number of highly informative features among many uninformative features.  JOFSTO's construction efficiently identifies potentially correlated, but effective subsets and returns a trained task network.  We demonstrate the approach using parameter estimation and mapping problems in quantitative MRI, where economical ED is crucial for clinical application.  Results from simulations and empirical data show the subsampling-task paradigm strongly outperforms classical ED, and within our paradigm, JOFSTO outperforms state-of-the-art supervised FS techniques.  JOFSTO extends immediately to wider image-based ED problems and other scenarios where the design must be specified globally across large numbers of acquisitions.  Our code is available for reviewers https://www.dropbox.com/scl/fo/qe6vb1w6fuf869hx4ht0k/h?dl=0&rlkey=og8czcorurl57jbiixio7hcjt 