High-pressure freezing (HPF) is capable of converting liquid water, to a depth of approx 0.6 mm, into amorphous ice nearly instantaneously. At midbody, an adult Caenorhabditis elegans hermaphrodite approaches its widest girth of approx 0.1 mm. In theory, an entire living adult animal can be physically immobilized instantly in amorphous ice by HPF, thus, providing a unique opportunity to examine cellular architecture with exquisite spatial preservation. The following chapter will discuss, in detail, procedures for freezing C. elegans under high pressure, for embedding frozen samples in resin after a freeze-substitution step, and for the postembedding immunogold labeling of proteins contained within thin sections of embedded animals. These protocols enable high-resolution analysis of both morphological features and molecular domains within most tissues of C. elegans.