  In this work we present a search for (solar) chameleons with the CERN Axion
Solar Telescope (CAST). This novel experimental technique, in the field of dark
energy research, exploits both the chameleon coupling to matter ($\beta_{\rm
m}$) and to photons ($\beta_{\gamma}$) via the Primakoff effect. By reducing
the X-ray detection energy threshold used for axions from 1$\,$keV to 400$\,$eV
CAST became sensitive to the converted solar chameleon spectrum which peaks
around 600$\,$eV. Even though we have not observed any excess above background,
we can provide a 95% C.L. limit for the coupling strength of chameleons to
photons of $\beta_{\gamma}\!\lesssim\!10^{11}$ for $1<\beta_{\rm m}<10^6$.
