An integrated master schedule (IMS) is a single network of horizontally and vertically integrated activities consistent with all authorized work for a project. This networked schedule includes all milestones documented in an integrated master plan (IMP) or project milestone hierarchy as well as the detailed activities to meet major project objectives or events, accomplishments, and completion criteria. The IMS depicts the sequence of how the work is planned to be accomplished based on the schedule calendar working days and required resources. The detailed activities are often resource loaded to provide the basis for the Earned Value Management System (EVMS) time phased budget and estimate to complete cost data. The schedule status data is also used as the basis for claiming earned value in the EVMS.

The detailed activities can be summarized as needed using the outline codes and other grouping criteria. Detailed activities may be grouped together into work packages, work packages into control accounts, and control accounts based on their respective CWBS element and/or project organizational element. Outline or milestone/activity attribute coding are used to uniquely identify external dependencies and interfaces to other systems for project specific reporting or other management needs. The IMS incorporates activities subcontractors are performing at some level of detail to adequately manage the entire scope of work. Supplemental schedules may also be used to inform the development of the IMS. This often occurs in a production environment where the production schedules provide the supporting data for summary work package activities in the IMS.

A properly constructed IMS provides the ability to identify critical milestones and supporting activities, summarize detailed schedule data to intermediate and total project levels, and to evaluate the impact of current schedule performance on future activities and events. Using a single IMS ensures top down and bottom up traceability as well as data consistency between levels. It should also be constructed to support government customer earned value management (EVM) data deliverable requirements as defined in the Integrated Program Management Report (IPMR) Data Item Description (DID) DI-MGMT-81861A and the Integrated Program Management Data and Analysis Report (IPMDAR) DID DI-MGMT-81861C.

Scheduling best practices are documented in industry guides such as the NDIA Integrated Program Management Division (IPMD) Planning and Scheduling Excellence Guide (PASEG) that describes eight essential scheduling principles or Generally Accepted Scheduling Principles (GASP). Another useful reference document is the Government Accountability Office (GAO) Schedule Assessment Guide: Best Practices for Project Schedules. The GAO Guide discusses ten best scheduling practices that help to ensure a reliable schedule is developed and maintained for the life of a project.