Problem definition:We study the practice-motivated problem of dynamically procuring a new, short life-cycle product under demand uncertainty. The firm does not know the demand for the new product but has data on similar products sold in the past, including demand histories and covariate information such as product characteristics.Academic/practical relevance: The dynamic procurement problem has long attracted academic and practitioner interest, and we solve it in an innovative data-driven way with proven theoretical guarantees.This work is also the first to leverage the power of covariate data in solving this problem.Methodology: We propose a new, combined forecasting and optimization algorithm called the Residual Tree method, and analyze its performance via epi-convergence theory and computations. Our method generalizes the classical Scenario Tree method by using covariates to link historical data on similar products to construct demand forecasts for the new product.Results: We prove, under fairly mild conditions, that the Residual Tree method is asymptotically optimal as the size of the data set grows. We also numerically validate the method for problem instances derived using data from the global fashion retailer Zara. We find that ignoring covariate information leads to systematic bias in the optimal solution, translating to a 6-15% increase in the total cost for the problem instances under study. We also find that solutions based on trees using just 2-3 branches per node, which is common in the existing literature, are inadequate, resulting in 30-66% higher total costs compared with our best solution.Managerial implications: The Residual Tree is a new and generalizable approach that uses past data on similar products to manage new product inventories. We also quantify the value of covariate information and of granular demand modeling.for apparel articles may include the procurement cost, retail price, colour, item type (e.g., sweater, t-shirt, etc.), fabric, design style (e.g., sporty, classic), expert predictions of the product's popularity, etc. We refer to covariates tied to product attributes that do not change over time as "static." Our approach can also account for "dynamic" covariates-e.g., lagged demand observations included to naturally account for demand auto-correlations. Importantly, covariates are essential for accounting for product heterogeneity by providing a means for aligning demand observations across different products. This allows us to construct a large number of estimated demand trajectories relevant to the new product, which we can then use in a scenario-based model of forecast updating dynamics.Our method employs a new approach which we call the Residual Tree method, which can be used to solve general multi-stage stochastic programs where there is no information about the