In this thesis, the CW and pulse EPR techniques are employed to understand several information, such as the local and electronic structure and magnetic interactions of metal ions in metalorganic frameworks as well as the guest-host framework interaction upon gas adsorption. Other characterization techniques, such as PXRD, SQUID, and quantum chemical calculation, are also outlined, which are complementary to the information provided by EPR. In situ EPR studies give valuable details on structural transition, which can’t be attained by other techniques always. EPR spectroscopy confirms that post-synthetic modification is possible in paddle wheel-based MOFs through the magnetic coupling of metal centers and also gives information about magnetic mixed paddle wheel units, which is often complicated to understand. The quite challenging divalent nickel-based MOF is studied along with NO adsorption, and the result highlights the capabilities of sophisticated EPR techniques in combination with quantum chemical calculations to provide fundamental insights into the non-obvious electronic structure of open-shell species docked in metal-organic frameworks. Finally, the inter- and intra-trimer interactions of high-spin chromium-based trimers are discussed in detail in combination with SQUID magnetometry.