The standard step-backwater method of computing water-surface profiles is described in this chapter. The hydraulic principles and assumptions are reviewed, and the field data requirements are described. Certain special cases of backwater curves and certain special field conditions are discussed in detail. The technique is used to establish or extend stage-discharge ratings; to define areas which will be innundated by flood flows of a given frequency; and to compute profiles through various reaches, including multichannel flows, and past control structures such as bridges, culverts, and road embankments. A brief description of analysis of floodways and effects of encroachments is also presented.