Title: Implicit Acceleration of Gradient Flow in Overparameterized Linear Models. Abstract: We study the implicit acceleration of gradient flow in over-parameterized two-layer linear models. We show that implicit acceleration emerges from a conservation law that constrains the dynamics to follow certain trajectories. More precisely, gradient flow preserves the difference of the Gramian~matrices of the input and output weights and we show that the amount of acceleration depends on both the magnitude of that difference (which is fixed at initialization) and the spectrum of the data. In addition, and generalizing prior work, we prove our results without assuming small, balanced or spectral initialization for the weights, and establish interesting connections between the matrix factorization problem and Riccati type differential equations.