||Phytotechnologies are a set of technologies using plants to remediate or contain contaminants in soil, groundwater, surface water, or sediments. These technologies have become attractive alternatives to conventional cleanup technologies due to relatively low capital costs and the inherently aesthetic nature of planted sites. This document provides guidance for regulators, who evaluate and make informed decisions on phytotechnology work plans, and for practitioners, who have to evaluate any number of remedial alternatives at a given site. This document is an update to Phytoremediation Decision Tree (PHYTO-1, 1999) and Phytotechnology Technical and Regulatory Guidance Document (PHYTO-2, 2001) and replaces the previous documents entirely. It merges the concepts of both previous documents and includes new and, more importantly, practical information on the process and protocol for selecting and applying various phytotechnologies as remedial alternatives. The technical descriptions of phytotechnologies in this document concentrate on the functioning mechanisms: phytosequestration, rhizodgradation, phytohydraulics, phytoextraction, phytodegradation, and phytovolatilization. For example, the application of phytotechnologies as a hydraulic control for groundwater is described as phytohydraulics (transpiration). This approach was selected to provide both scientific accuracy and a basic understanding of these mechanisms to the reader. Decision trees (Remedy Selection, Groundwater, Soil/Sediment, and Riparian Zone) help guide the user through the application of phytotechnologies to a remediation project.