Peacebuilding is an activity that aims to resolve injustice in nonviolent ways and to transform the cultural and structural conditions that generate deadly or destructive conflict. It revolves around developing constructive personal, group, and political relationships across ethnic, religious, class, national, and racial boundaries. The process includes violence prevention; conflict management, resolution, or transformation; and post-conflict reconciliation or trauma healing before, during, and after any given case of violence.

As such, peacebuilding is a multidisciplinary cross-sector technique or method that becomes strategic when it works over the long run and at all levels of society to establish and sustain relationships among people locally and globally and thus engenders sustainable peace. Strategic peacebuilding activities address the root or potential causes of violence, create a societal expectation for peaceful conflict resolution, and stabilize society politically and socioeconomically.

The methods included in peacebuilding vary depending on the situation and the agent of peacebuilding. Successful peacebuilding activities create an environment supportive of self-sustaining, durable peace; reconcile opponents; prevent conflict from restarting; integrate civil society; create rule of law mechanisms; and address underlying structural and societal issues. Researchers and practitioners also increasingly find that peacebuilding is most effective and durable when it relies upon local conceptions of peace and the underlying dynamics that foster or enable conflict.

The definition of peacebuilding varies depending on the actor, with some definitions specifying what activities fall within the scope of peacebuilding or restricting peacebuilding to post-conflict interventions. Even if peacebuilding has remained a largely amorphous concept without clear guidelines or goals, common to all definitions is the agreement that improving human security is the central task of peacebuilding. In this sense, peacebuilding includes a wide range of efforts by diverse actors in government and civil society at the community, national, and international levels to address the root causes of violence and ensure civilians have freedom from fear (negative peace), freedom from want (positive peace) and freedom from humiliation before, during, and after violent conflict.

Although many of peacebuilding's aims overlap with those of peacemaking, peacekeeping and conflict resolution, it is a distinct idea. Peacemaking involves stopping an ongoing conflict, whereas peacebuilding happens before a conflict starts or once it ends. Peacekeeping prevents the resumption of fighting following a conflict; it does not address the underlying causes of violence or work to create societal change, as peacebuilding does. Peacekeeping also differs from peacebuilding in that it only occurs after conflict ends, not before it begins. Conflict resolution does not include some components of peacebuilding, such as state building and socioeconomic development.

While some use the term to refer to only post-conflict or post-war contexts, most use the term more broadly to refer to any stage of conflict. Before conflict becomes violent, preventive peacebuilding efforts, such as diplomatic, economic development, social, educational, health, legal and security sector reform programs, address potential sources of instability and violence. This is also termed conflict prevention. Peacebuilding efforts aim to manage, mitigate, resolve and transform central aspects of the conflict through official diplomacy; as well as through civil society peace processes and informal dialogue, negotiation, and mediation. Peacebuilding addresses economic, social and political root causes of violence and fosters reconciliation to prevent the return of structural and direct violence. Peacebuilding efforts aim to change beliefs, attitudes and behaviors to transform the short and long term dynamics between individuals and groups toward a more stable, peaceful coexistence. Peacebuilding is an approach to an entire set of interrelated efforts that support peace.

Peace-building is a term of more recent origin that, as used in the report of the Panel on United Nations Peace Operations (2000), defines "activities undertaken on the far side of conflict to reassemble the foundations of peace and provide the tools for building on those foundations something that is more than just the absence of war. "

In 2007, the UN Secretary-General's Policy Committee defined peacebuilding as follows: "Peacebuilding involves a range of measures targeted to reduce the risk of lapsing or relapsing into conflict by strengthening national capacities at all levels for conflict management, and to lay the foundations for sustainable peace and sustainable development. Peacebuilding strategies must be coherent and tailored to specific needs of the country concerned, based on national ownership, and should comprise a carefully prioritized, sequenced, and therefore relatively narrow set of activities aimed at achieving the above objectives."