This document, "Book Two of Four: Planning and Developing an LDS", is the second installment of this Forum (National Forum on Education Statistics) series of guides on longitudinal data systems (LDS). This second book in the guide series delves into the planning, implementation, and evaluation phases of a longitudinal data system (LDS) project. It guides readers through the process of engaging a wide variety of stakeholders to create a vision for an LDS, build support for the undertaking, develop the system, and gauge how well it is meeting intended goals. Chapter 1 introduces the information life cycle, a helpful concept when developing any data system. Chapter 2 discusses the systems development life cycle, another useful concept for developing a data system. Chapter 3 discusses the people and processes that characterize effective project management of an LDS development effort. Chapter 4 provides guidance on engaging stakeholders to define the organization's vision for an LDS that will meet end users' needs. Chapter 5 discusses the critical relationship between the state education agency (SEA) and districts, and offers best practices on how to strengthen these ties. Chapter 6 discusses the self-assessment phase of the effort, during which an agency should identify its current system and functionalities. Chapter 7 presents the concept of "enterprise architecture", a helpful framework for planning and evaluating the agency's current and desired data systems. Chapter 8 discusses the needs-assessment phase, during which an agency should define its desired system based on stakeholder requirements. Chapter 9 addresses how to identify the data elements that need to be collected to meet the stakeholders' information needs. Chapter 10 covers the important issues of interoperability and portability. Chapter 11 discusses strategies for gaining sustained support for the system. Chapter 12 addresses the need for, and approaches to, promoting the LDS and gaining grassroots support. Chapter 13 discusses the choice between building an LDS in-house and hiring a vendor, addressing some of the pros and cons of each approach. Chapter 14 provides an introduction to effective request for proposals (RFP) writing. Chapter 15 addresses system evaluation, during which an agency assesses the "success" of the system based on many criteria. Findings should inform iterative system refinement. Appendices include: (1) Overview of the LDS Guide Series; (2) References; (3) Additional Resources; (4) Information Technology Audits; (5) Forum and Other NCES. (Contains 5 tables and 4 figures.) [For "Traveling through Time: The Forum Guide to Longitudinal Data Systems. Book One of Four: What Is an LDS? NFES 2010-805", see ED511638.]