Blue Effect (rarely called Modr? Efekt and M.Efekt) is renewed progressive rock band from Czech Republic. Guitarist Radim Hladík was the most prominent member, and some releases were credited to Modr? Efekt and Radim Hladik, though much confusion surrounds the naming of this band. Several of their earlier releases translate the name to Blue Effect; some use Modr? Efekt; still others shorten the name to M. Efekt.
Starting with Meditace in 1969 (as Blue Effect), the band released approximately ten albums, culminating with 33 in 1980. Aside from Hlad?k, drummer Vlado ?ech was the only other musician to figure in the entire history of the band. Lešek Semelka played keyboards from 1971 on. Other musicians varied.