Tissue engineering faces significant challenges in vascularizing tissues in vitro and in vivo, primarily due to limitations in nutrient and oxygen diffusion, which restricts construct size and integration with host vasculature. This review outlines current strategies for vascularization, including scaffold functionalization, cell-based techniques, bioreactor designs, microelectromechanical systems (MEMS)-related approaches, modular assembly, and in vivo systems. Each approach aims to improve oxygen and nutrient transport, reduce gradients, and enable functional anastomosis with host vessels. Scaffold functionalization involves loading or coupling with angiogenic factors like VEGF, bFGF, and PDGF, or engineering scaffolds with microchannels or porous structures to enhance perfusion. Bioreactors facilitate improved nutrient and oxygen transport through perfusion, rotating systems, and spinner flasks. MEMS-related approaches use microfluidic systems to replicate microvascular networks, often with degradable materials. Modular assembly combines minimal functional units, such as endothelial cell-coated hydrogels, to build larger vascular networks. In vivo systems, like AV loops and polysurgery techniques, utilize host vasculature to vascularize engineered tissues. Growth factor delivery is critical for vascularization, with techniques ranging from scaffold loading to microsphere encapsulation. Biodegradable microfluidics offer promising alternatives to nondegradable materials like PDMS, enabling controlled release of growth factors and better vascularization. Cell-based techniques, including endothelial cell cocultures and growth factor-producing cells, provide functional vasculature but face challenges in functional anastomosis. Bioreactors, such as rotating and perfusion systems, improve tissue viability but lack vascular integration. MEMS-based microfluidics enable precise control over vascular networks, though challenges remain in in vivo integration. Modular assembly and in vivo systems, such as AV loops, offer potential for functional anastomosis and vascular integration. Oxygen modeling and measurement are essential for understanding vascularization, with Fick's law and Michaelis-Menten kinetics used to predict oxygen distribution and consumption. These models help optimize scaffold design and vascular integration, ensuring adequate oxygen supply for tissue viability. Overall, the field requires continued innovation in vascularization strategies to achieve clinically relevant tissue engineering.Tissue engineering faces significant challenges in vascularizing tissues in vitro and in vivo, primarily due to limitations in nutrient and oxygen diffusion, which restricts construct size and integration with host vasculature. This review outlines current strategies for vascularization, including scaffold functionalization, cell-based techniques, bioreactor designs, microelectromechanical systems (MEMS)-related approaches, modular assembly, and in vivo systems. Each approach aims to improve oxygen and nutrient transport, reduce gradients, and enable functional anastomosis with host vessels. Scaffold functionalization involves loading or coupling with angiogenic factors like VEGF, bFGF, and PDGF, or engineering scaffolds with microchannels or porous structures to enhance perfusion. Bioreactors facilitate improved nutrient and oxygen transport through perfusion, rotating systems, and spinner flasks. MEMS-related approaches use microfluidic systems to replicate microvascular networks, often with degradable materials. Modular assembly combines minimal functional units, such as endothelial cell-coated hydrogels, to build larger vascular networks. In vivo systems, like AV loops and polysurgery techniques, utilize host vasculature to vascularize engineered tissues. Growth factor delivery is critical for vascularization, with techniques ranging from scaffold loading to microsphere encapsulation. Biodegradable microfluidics offer promising alternatives to nondegradable materials like PDMS, enabling controlled release of growth factors and better vascularization. Cell-based techniques, including endothelial cell cocultures and growth factor-producing cells, provide functional vasculature but face challenges in functional anastomosis. Bioreactors, such as rotating and perfusion systems, improve tissue viability but lack vascular integration. MEMS-based microfluidics enable precise control over vascular networks, though challenges remain in in vivo integration. Modular assembly and in vivo systems, such as AV loops, offer potential for functional anastomosis and vascular integration. Oxygen modeling and measurement are essential for understanding vascularization, with Fick's law and Michaelis-Menten kinetics used to predict oxygen distribution and consumption. These models help optimize scaffold design and vascular integration, ensuring adequate oxygen supply for tissue viability. Overall, the field requires continued innovation in vascularization strategies to achieve clinically relevant tissue engineering.