In this chapter, the URANS closure modeling is presented using one or more balance equations for the characteristic quantities of turbulence. In Sect. 8.1, an introduction is presented. In Sect. 8.2, a model composed of one balance equation is presented, called the \({\varvec{k}}{{-}}\ell\) model. Still in this item, the \({\varvec{S}}{{-}}{\varvec{A}}\) model is presented, also with a balance equation. In Sect. 8.3, some closure models for two balance equations are presented, including the \({\varvec{k}}{{-}}{\varvec{\varepsilon}}\) model and the \({\varvec{k}}{{-}}{\varvec{\omega}}{{-}}{\varvec{SST}}\) model. In Sect. 8.4, the \({\varvec{RSM}}\) model is presented, which is composed of 17 balance equations, including thermal effects. In Sect. 8.5, the \({\varvec{IASM}}\) model is presented as well as the \({\varvec{EASM}}\) model. In Sect. 8.6, a performance analysis of the \({\varvec{URANS}}\) closure models is carried out. This chapter ends with a list of exercises.