Many network topologies lead to situations where transport protocol proxying is beneficial. For example, proxying enables endpoints to communicate when end-to-end connectivity is not possible, or to apply additional encryption where desirable (such as a VPN). Proxying can also improve client privacy, e.g., by hiding a client's IP address from a target server. Proxying technologies such as SOCKS and HTTP(S) CONNECT exist, albeit with their own shortcomings. For example, SOCKS signalling is not encrypted and HTTP CONNECT is currently limited to TCP. In contrast, HTTP/3 is a viable candidate protocol for proxying arbitrary traffic, as in a single connection it provides secure connectivity, multiplexed streams, address migration, and a unified congestion controller. An HTTP/3 datagram construct built on top of QUIC datagram frames would provide for unreliable data transmission and enable transporting UDP and other unreliable flows via a proxy. Moreover, it would not introduce potentially redundant or unnecessary recovery mechanisms. Lastly, HTTP supports an established request/response semantic that can set up and configure flows for different services. The primary goal of this working group is to develop mechanism(s) that allow configuring and concurrently running multiple proxied stream- and datagram-based flows inside an HTTPS connection. These mechanism(s) are collectively called MASQUE. The group will specify HTTP and/or HTTP/3 extensions to enable this functionality. The group will focus on a limited set of client-initiated services: (1) UDP CONNECT and (2) IP proxying. Server-initiated services are out of scope. The working group will first deliver a protocol solution for UDP CONNECT and a requirements document for IP proxying. Once both are complete, the working group will focus on a protocol solution for IP proxying. The working group will consider fallback to versions of HTTPS that operate over TCP as a mitigation to UDP or HTTP/3 blocking. Moreover, the working group will consider implications of tunneling protocols with congestion control and loss recovery over MASQUE, and may issue recommendations accordingly. New congestion control and loss recovery algorithms are out of scope. Multicast support is out of scope. However, the group may specify extension points that would enable future work on multicast. Specifying proxy server discovery mechanisms is also out of scope. However, the group may consider features, such as proxy server identifiers, that aid future discovery mechanisms. Impacts on address migration, NAT rebinding, and future multipath mechanisms of QUIC are not anticipated. However, the working group should document these impacts, or those of any other QUIC developments, if they arise. The group will coordinate closely with other working groups responsible for maintaining relevant protocol extensions, such as HTTPBIS, QUIC, or TLS. It will also coordinate closely with ICCRG and TSVWG on congestion control and loss recovery considerations, and intarea for IP Proxying.