AGENCY: Securities and Exchange Commission. ACTION: Concept release; request for comments. SUMMARY: The Securities and Exchange Commission (âCommissionâ) is conducting a broad review of the current equity market structure. The review includes an evaluation of equity market structure performance in recent years and an assessment of whether market structure rules have kept pace with, among other things, changes in trading technology and practices. To help further its review, the Commission is publishing this concept release to invite public comment on a wide range of market structure issues, including high frequency trading, order routing, market data linkages, and undisplayed, or âdark,â liquidity. The Commission intends to use the publicâs comments to help determine whether regulatory initiatives to improve the current equity market structure are needed and, if so, the specific nature of such initiatives. DATES: Comments should be received on or before April 21, 2010. http://www.sec.gov/rules/concept/2010/34-61358.pdf