When you ask America?s most seasoned and effective K-12 education givers which philanthropic investments have been most transformative over the last generation, charter schools rank at or near the top. For all of the inconsistency that exists within the sector, it has proven to be the laboratory, workhorse, and guiding light of K-12 education. Thousands of charter schools around the nation offer dramatically better options than students would otherwise receive. This is especially true for students from lower-income neighborhoods. Charters are expanding rapidly. For the sector to live up to its creed?autonomy to develop schools that perform better than traditional options, in exchange for accountability for results?philanthropists must make quality the watchword. Charter schooling is not without its failures and pitfalls. Philanthropists investing in charters must give in a wise and informed way. Donors large and small, many profiled in this guidebook, have shown that philanthropy can fuel sustained charter school growth. The most sophisticated use their giving to also undergird excellence, and shape public policy to promote innovation, autonomy, and accountability. The flowering of charter schools has been led by philanthropy, and donors must continue in their leading role if today?s millions of children still unable to access a quality education are to gain a better option. Exciting work remains.