Participatory design (originally co-operative design or design participation, now often co-design and also co-creation) is an approach to design that attempts to involve a variety of stakeholders (e.g. employees, partners, customers, citizens, end users) in the design process to help ensure the result meets their needs and is usable. Participatory design is an approach which is focused on processes and procedures of design and is not a design style. The term is used in a variety of fields, e.g. software design, urban design, architecture, landscape architecture, product design, sustainability, graphic design, industrial design, planning, and health services development, as a way of creating environments that are more satisfactory and appropriate to their inhabitants' and users' practical, cultural, emotional and spiritual needs. It is also one approach to placemaking.

Participatory design has been used in many settings and at various scales. For some, this approach has a political dimension of user empowerment and democratization. This inclusion of external parties in the design process does not excuse designers of their responsibilities. In their article "Participatory Design and Prototyping", Wendy Mackay and Michel Beaudouin-Lafon support this point by stating that "[a] common misconception about participatory design is that designers are expected to abdicate their responsibilities as designers and leave the design to users. This is never the case: designers must always consider what users can and cannot contribute."

In participatory design, participants (putative, potential or future) are invited to cooperate with designers, researchers and developers during certain parts of a design process. The broader definition of co-design requires the end user's participation not only in evaluating proposals but also in idea generation. Potentially, they participate during several stages of an innovation process: during the initial exploration and problem definition both to help define the problem and to focus ideas for solution, and, during development, they help evaluate proposed solutions.

In the broader discourse on collaborative processes, terminology such as co-design, co-creation, and urban co-creation is often debated and differentiated. For example, In "Co-designing for Society", Deborah Szebeko and Lauren Tan list various precursors of co-design, and differentiate co-design from participatory design because co-design "includes all stakeholders of an issue not just the users, throughout the entire process from research to implementation."

Similarly, Maria Gabriela Sanchez and Lois Frankel proposed that "Co-design may be considered . . . as an interdisciplinary process that involves designers and non-designers in the development of design solutions" and that "the success of the interdisciplinary process depends on the participation of all the stakeholders in the project".

According to Elizabeth Sanders and Pieter Stappers "Co-creation is a very broad term with applications ranging from the physical to the metaphysical and from the material to the spiritual", with co-design being a specific instance of co-creation.

Within urban studies, urban co-creation has been proposed to describe participatory processes that are genuinely inclusive, emphasizing the active, bottom-up involvement of residents, communities, and grassroots organizations in shaping urban environments. Seve et al. (2022) argue that urban co-creation encompasses a wide range of practices—including appropriation of space, self-construction, guerrilla gardening, and tactical urbanism—that challenge traditional top-down models. They contend that the term participation alone is ambiguous and insufficient to describe the diversity of collaborative practices and dynamics in urban transformation.

As described by Sanders and Stappers, one could position co-design as a form of human-centered design across two different dimensions. One dimension is the emphasis on research or design, another dimension is how much people are involved. Therefore, there are many forms of co-design, with different degrees of emphasis on research or design and different degrees of stakeholder involvement. For instance, one of the forms of co-design which involves stakeholders strongly early at the front end design process in the creative activities is generative co-design. Generative co-design is increasingly being used to involve different stakeholders, such as patients, care professionals and designers actively in the creative making process to develop health services.