Multiprotocol Label Switching (MPLS) is emerging as a flexible technology that can transport voice, IPv4, IPv6, layer 2 services (Frame Relay, ATM, Ethernet, etc.), and even PDH and SDH/SONET circuits over a single packet infrastructure, in a new attempt to solve the old problem of network convergence. MPLS traffic engineering, quality of service support (in combination with DiffServ), and fast restoration capabilities can be used to provide each service with strict service-level agreements (SLAs) in a cost-efficient way. Several standardization and industry organizations are contributing to this goal. This article reviews current activities in the IETF, MPLS/Frame Relay Alliance, and ITU-T related to transport over MPLS, comparing their approaches, identifying overlaps, and open issues.