According to the PMBOK® Guide, specifically within the Develop Schedule process, Resource Leveling is a resource optimization technique used to adjust the start and finish dates of activities to address resource constraints.

Sequential Application: In the standard flow of schedule development, the project manager first performs Critical Path Method (CPM) analysis to determine the theoretical shortest duration of the project based on logical dependencies and constraints.

Addressing Over-allocation: Once the critical path is identified, the project manager often finds that certain resources are " over-allocated " (assigned to multiple tasks at the same time) or that resource demand exceeds available supply. Resource leveling is then applied to resolve these conflicts.

Impact on the Schedule: Because resource leveling prioritizes resource availability, it often results in the original critical path changing or the project duration increasing. It is essentially the process of making the " ideal " schedule (the CPM) " realistic " based on the actual people and equipment available.

Resource Smoothing: A related technique, resource smoothing, is also applied after CPM analysis but only adjusts activities within their " float " so as not to affect the critical path or the completion date.

Comparison with other options:

A. Before constraints have been identified: This is illogical. Resource leveling is the response to resource constraints. You cannot level resources until you know what those constraints are.

B. Before it has been analyzed by the critical path method: If you level before CPM analysis, you won ' t know which activities are critical versus which ones have flexibility (float). You need the CPM " baseline " to understand the impact of your leveling decisions.

D. After critical activities have been removed from the critical path: Critical activities are not " removed " from the critical path; the path itself is a calculation of the longest sequence. While leveling might change which activities are on the critical path, you don ' t remove activities to perform leveling.