Spacetime-filling branes and strings with sixteen supercharges

We discuss branes whose worldvolume dimension equals the target spactime dimension, i.e. 'spacetime-filling branes'. In addition to the D9-branes, there are 9-branes in the NS-NS sectors of both the IIA and IIB strings. Each of these types of branes is used in the construction of a string theory with sixteen supercharges by modding out a type II string by an appropriate discrete symmetry and adding 32 9-branes. These constructions are related by a web of dualities and each arises as a different limit of the Horava-Witten construction.