Low Impact Development (LID) techniques for a natural systems approach to stormwater management used to be a best practice that forward-thinking land developers employed to conserve natural and financial resources. As the understanding of the significant impacts of untreated stormwater on our waterways deepens, however, federal and state regulators have begun to require LID. Low Impact Development approaches the management of stormwater as an integral part of the site design and planning process - not merely as an exercise in sizing storm drains and detention ponds after the site design has been completed. An LID approach, if implemented successfully, allows for maximization of land development potential, while preserving ecosystem function of the natural environment and the health of our communities. Creative, context-based site planning and the use of small, decentralized treatment and infiltration techniques enables site engineers to fulfill the mission of Low Impact Development: maintaining natural hydrology, while successfully managing on-site stormwater runoff volume, peak rate, and water quality. There is a wide array of impact reduction and site design techniques that allow the site planner/engineer to create stormwater control mechanisms that function in a manner similar to that of natural systems. Last November, the Massachusetts Department of Environmental Protection (DEP) proposed a new statewide Stormwater General Permit (SGP) which significantly increases the requirements for treatment. The proposed program would apply to private properties statewide with impervious areas greater than 5 acres and to private properties in the Charles River watershed with impervious areas greater than 2 acres. Most importantly, the proposed rules require retrofit of existing properties, not just new development. Concurrently, the US Environmental Protection Agency (EPA) is issuing the second 5-year MS4 permit, which regulates municipal separate storm sewer systems (MS4s) in urbanized areas. Understandably, the development community is quite concerned about the fiscal impacts of these proposed rules. On Friday, May 29, at the Sheraton Hotel in Framingham, Mass., the Environmental Business Council is presenting its 3rd Annual Low Impact Development Conference. Given the shift of LID from a voluntary best management practice to a requirement, the focus this year is on "Regulatory Drivers". The half-day conference will provide the latest information on where the regulations are going, and the developing science and economics behind those regulations. The conference includes speakers from the Executive Office of Energy and Environmental Affairs, EPA, DEP, and UNH, among others, and will also feature a vendor fair which will showcase companies demonstrating innovative technologies and services. This is a must attend event for developers, consultants, architects, engineers, regulators, and municipal, state, and federal officials. Leo Pierre Roy, LEED AP, is principal of VHB/Vanasse Hangen Brustlin, Inc., Watertown, MA.