The Mercedes-Benz O405 was a model of integral single-decker bus produced by Mercedes-Benz between 1983 and 2001. The O405 replaced the O305 and was replaced by the Citaro (O530) family after an eighteen-year production run.

There were three major product lines in the O405 family - these were high-floor (O405), low-floor (O405N) and low-entry (O405NH) versions. All versions were also available as articulated buses (the O405G, O405GN and O405GNH respectively).

The O405 family was one of the best-selling Mercedes-Benz products in British bus history. As well as integral Mercedes-Benz bodies, the family were available with Wright Cityranger and Optare Prisma bodies. Eventually 364 members of the O405 family were sold in the United Kingdom alone - 203 O405Ns, 145 O405s and sixteen O405G/O405GNs. The first, an O405G registered K1GRT, was sold to Grampian in November 1992 and the last, an O405GN registered DCZ3103, was sold to Citybus in March 2000.

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