Planning is the process of stating goals and determining the most effective way of reaching them. In project management, planning involves defining the project scope, objectives, and determining the steps necessary to achieve the desired outcomes. This includes identifying resources, establishing timelines, and creating a strategy to ensure that the project is completed on time, within budget, and to the required quality standards.

Option A: Implementingrefers to the execution phase, where the plans are put into action.

Option B: Mission Statementis a brief statement that defines the purpose or core values of an organization but is not a process.

Option C: Managinginvolves overseeing and coordinating the various aspects of a project, typically during the execution phase.

Thus,D. Planningis the correct answer as it is the process of stating goals and determining the methods to achieve them.