In this collection of research projects, we take a layered approach to foundational verification of correctness and accuracy of numerical software–that is, formal machine-checked proofs about programs (not just algorithms), with no assumptions except specifications of instruction-set architectures. We build, improve, and use appropriate tools at each layer: proving in the real numbers about discrete algorithms; proving how floating-point algorithms approximate real-number algorithms; reasoning about C program implementation of floating-point algorithms; and connecting all proofs end-to-end in Coq.