The waste management is in need of a reliable and economical treatment method for metals in fly ashes from municipal solid waste incineration (MSWI). However, no state-of-the-art technique has gained wide acceptance yet. This Doctoral Thesis aimed at assessing the possibilities and limitations of carbonation as a stabilization method. Factors that were studied are the partial pressure of carbon dioxide, the addition of water, the temperature, and the reaction time. Laboratory experiments were performed applying methods such as factorial experimental design, thermal analysis, scanning electron microscopy (SEM), x-ray diffraction (XRD), and leaching assays including titration at static pH and sequential extraction. Leaching data were verified and complemented using chemical equilibrium calculations. Data evaluation was performed by means of multivariate statistics such as multiple linear regression, principal component analysis (PCA), and partial least squares (PLS) modeling. It was found that carbonation is a good prospect for a stabilization technique especially with respect to the major pollutants lead (Pb) and zink (Zn). However, a mobilization of cadmium (Cd) was observed, which requires further research on possible countermeasures such as e.g. metal demobilization through enhanced silicate formation.