Ribosomes are molecular machines found within all cells. They perform protein synthesis, translating instruction-sequences carried by mRNA strands into proteins. The instructions carried by the mRNA strands have been read from the cell's DNA strand by other molecular machines, in a process known as transcription.

With the help of tRNA molecules, ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules. When strung together in the specified order, the amino acids form polypeptide chains (unfolded protein molecules). These, in turn form all biological components, including the molecular machines found within cells.

Ribosomes consist of two major components: the small and large ribosomal subunits. These come together when needed to convert mRNA instruction strands into unfolded proteins.

Ribosomes and their associated molecules are sometimes referred to as the translational apparatus.