Matrix invasion by a tumor cell requires the degradation of components in the extracellular matrix (ECM) as one of the initial steps in the metastatic process. Tumors cells achieve ECM invasion primarily through the overexpression of matrix metalloproteinases (MMPs), a family of enzymes that function to degrade ECM proteins. In this chapter, an in vitro collagen degradation assay and a modified collagen invasion assay system are described. The collagen degradation assay is a simple method to measure the ability of tumor cells to degrade type I collagen, the main constituent of the stromal compartment, in a 3-D matrix environment. The modified collagen invasion assay system enables researchers to study the effects of transient overexpression and/or targeted knockdown (as with siRNAs) of a given gene on collagen invasion of tumor cells in a real-time format.