Measurements on the correlation between stress, strain and magnetic anisotropy of epitaxial monolayers are performed in this work. To this end, mechanical stress during film growth and stress during magnetization processes are measured directly by the optical cantilever curvature technique. Epitaxial misfit induced film stress is measured for Fe, Ni and Co monolayers on Ir(100). Film stresses of the order of several GPa are detected, which are ascribed to the epitaxial misfit. The stress measurements also indicate structural and morphological changes in the growing film. The first 2 monolayers of Fe on Ir(100) can be described as a fcc precursor, which serve as a template for the subsequent growth of bcc Fe at higher thickness. Ni and Co are found to grow in a fcc phase on Ir. The results on the magnetoelastic stress indicate that the magnetoelastic coupling coefficients B1eff and B2eff of Fe, Ni and Co deviate sharply from the respective bulk behavior, and they suggest that strain may play an important role for this non-bulklike magnetoelastic behavior. The role of this non-linear magnetoelastic coupling for the magnetic anisotropy of ferromagnetic monolayers is studied. The magnetic anisotropy for out-of-plane magnetization is analyzed. MOKE measurements reveal that the easy magnetization axis is in-plane for Fe and Co films on Ir(100), and changes from outof- plane to in-plane for Ni at about 15 ML for increasing film thickness. These experimental observations can be well described by the measured magnetoelastic coupling coefficients. The relation between surface stress and surface reconstruction of the Ir(100)surface is investigated by adsorbate-induced stress measurements and low energy electron diffraction (LEED). During the H-induced surface reconstruction from Ir(100)-(5×1)Hex to Ir(100)-(5×1)-H, a compressive stress change of -1.75 N/m is obtained. LEED spot intensities for integer and fractional order spots are measured during reconstruction, and their intensities identify the progress of the surface reconstruction during H exposure. A direct correlation between the surface stress change and the spot intensity ratio (Iint/Ifrac) is established, which shows a linear dependence, suggesting that surface stress should be considered as an important factor during this reconstruction. The stress change during formation of CoO(111) is measured during the oxidation of 2 monolayers Co. LEED identifies the c(10x2) structure of the CoO(111) film, which is under a tensile stress of +2.1 N/m. The magnitude of this stress can be quantitatively ascribed to the anisotropic lattice misfit between CoO(111) and Ir(100). This first stress measurement on an oxide surface suggests that Coulomb-interactions within the presumably polar CoO(111) layers do not contribute to the oxide film stress.