This paper reports the first experimental realization of entanglement using the orbital angular momentum (OAM) of photons, which are states of the electromagnetic field with phase singularities (doughnut modes). Unlike previous experiments that used photon polarization to create qubit entanglement, this study demonstrates multi-dimensional entanglement where the entangled states consist of many orthogonal states. This opens new possibilities for quantum computation and communication, such as quantum cryptography with higher alphabets, which could increase information flux through communication channels. The experiment confirmed that spontaneous parametric down-conversion conserves the OAM of photons. This was verified by investigating three cases for pump photons with OAM of -ħ, 0, and ħ per photon. The results showed that the down-converted photons are in a coherent superposition of allowed combinations, indicating entanglement in their OAM. The conservation of OAM was further confirmed by measuring high signal-to-noise ratios, showing that the OAM of the down-converted photons equals that of the pump photons. The study also demonstrated entanglement between two photons produced in the conversion process. The two-photon state was found to be a coherent superposition of product states of various Gaussian and LG modes, which obey angular momentum conservation. This is in contrast to classical correlation, which would result in an incoherent mixture. The results confirm that the OAM is conserved in parametric down-conversion, and that the two-photon state is entangled. The paper also discusses the potential applications of these photon states in quantum cryptography, quantum teleportation, and optical tweezers. The results suggest that entanglement of higher-dimensional quantum systems is a promising area for future research, with potential applications in quantum communication and information. The study was supported by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung (FWF).This paper reports the first experimental realization of entanglement using the orbital angular momentum (OAM) of photons, which are states of the electromagnetic field with phase singularities (doughnut modes). Unlike previous experiments that used photon polarization to create qubit entanglement, this study demonstrates multi-dimensional entanglement where the entangled states consist of many orthogonal states. This opens new possibilities for quantum computation and communication, such as quantum cryptography with higher alphabets, which could increase information flux through communication channels. The experiment confirmed that spontaneous parametric down-conversion conserves the OAM of photons. This was verified by investigating three cases for pump photons with OAM of -ħ, 0, and ħ per photon. The results showed that the down-converted photons are in a coherent superposition of allowed combinations, indicating entanglement in their OAM. The conservation of OAM was further confirmed by measuring high signal-to-noise ratios, showing that the OAM of the down-converted photons equals that of the pump photons. The study also demonstrated entanglement between two photons produced in the conversion process. The two-photon state was found to be a coherent superposition of product states of various Gaussian and LG modes, which obey angular momentum conservation. This is in contrast to classical correlation, which would result in an incoherent mixture. The results confirm that the OAM is conserved in parametric down-conversion, and that the two-photon state is entangled. The paper also discusses the potential applications of these photon states in quantum cryptography, quantum teleportation, and optical tweezers. The results suggest that entanglement of higher-dimensional quantum systems is a promising area for future research, with potential applications in quantum communication and information. The study was supported by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung (FWF).