The Maximality Principle \mathrm{MP_{CCC}} is a scheme which states that if a sentence of the language of ZFC is
true in some CCC forcing extension V^\mathbb{P} , and remains true in any further CCC-forcing extension of V^\mathbb{P} , then it is true in all CCC-forcing extensions of V, including
V itself. A parameterized form of this principle, \mathrm{MP_{CCC}}(\mathbb{R}) , makes this assertion for formulas taking real parameters. In this
paper, we show that \mathrm{MP_{CCC}}(\mathbb{R}) has the same consistency strength as ZFC, solving an open problem of
Hamkins. We extend this result further to parameter sets larger than .