The Nuveen S&P 500 Dynamic Overwrite Fund (NYSE:SPXX) invests in S&P 500 components and writes covered calls on 35% - 75% of its holdings. Doing so boosts the fund's distribution yield to 7.6%, but moderately reduces potential capital gains. SPXX's strategy seems reasonably sustainable, with fund distributions and NAVs seeing positive growth since 2009, although both were down during the past financial crisis. SPXX's strong 7.6% distribution yield and compelling 9.2% discount to NAV make the fund a buy.