Endothelial dysfunction is a critical factor in the development and progression of cardiovascular disease (CVD) and its complications. This review discusses the molecular mechanisms underlying endothelial dysfunction, including nitric oxide (NO) availability, oxidative stress, and inflammation-mediated pathways. It also explores the impact of endothelial dysfunction on various pathological conditions such as atherosclerosis, heart failure, diabetes, hypertension, chronic kidney disease (CKD), and neurodegenerative diseases. The review summarizes traditional and novel potential biomarkers of endothelial dysfunction and pharmacological and nonpharmacological therapeutic strategies for its prevention and treatment. The review highlights the importance of understanding emerging biomarkers and therapeutic approaches to reduce the risk of CVD and its complications. Endothelial dysfunction is primarily caused by an imbalance between antioxidant defense mechanisms and reactive oxygen species (ROS) generation, leading to vascular damage. ROS and heightened oxidative stress play a crucial role in the development of endothelial dysfunction, as ROS serve as significant second messengers in cellular signaling. Inflammatory stimuli, including proinflammatory cytokines and cardiovascular risk factors, activate proinflammatory signaling pathways in endothelial cells (EC), leading to the upregulation of adhesion molecules. The main mechanisms of endothelial dysfunction involve impaired NO bioavailability and signaling pathways, oxidative stress, and inflammation-mediated pathways. NO is synthesized by three distinct subtypes of NO synthase (NOS) enzymes: inducible NOS (iNOS), endothelial NOS (eNOS), and neuronal NOS (nNOS). The production of NO occurs through the catalysis of L-arginine (L-Arg) and O₂ by NOS in EC, a process that necessitates the involvement of various cofactors. The NO-sGC-cGMP signaling pathway plays a crucial role in cardiovascular, renal, and metabolic functions. Endothelial dysfunction is also associated with oxidative stress, which can be mitigated by antioxidants and other therapeutic approaches. Inflammation-mediated pathways contribute to endothelial dysfunction by promoting the adhesion of monocytes and neutrophils to the walls of arteries. Endothelial dysfunction occurs due to perturbations in oxidative stress, inflammation, and pathophysiological shear stress, leading to a reduction in antithrombotic and anti-inflammatory functions, as well as degradation of the glycocalyx. The dysfunctional EC adopts a proinflammatory and prothrombotic phenotype, characterized by decreased production of prostacyclin and NO, and increased release of proinflammatory and prothrombotic molecules. Endothelial dysfunction is a significant contributor to multiple CVD and related complications. In heart failure (HF), endothelial dysfunction is associated with impaired vascular tone, myocardial remodeling, and abnormal cell proliferation. In atherosclerosis, endothelial dysfunction facilitates the infiltration of LDL into the subendothelial layer, leading to its accumulation and oxidation to ox-LDL. This process triggers the expression of cell adhesionEndothelial dysfunction is a critical factor in the development and progression of cardiovascular disease (CVD) and its complications. This review discusses the molecular mechanisms underlying endothelial dysfunction, including nitric oxide (NO) availability, oxidative stress, and inflammation-mediated pathways. It also explores the impact of endothelial dysfunction on various pathological conditions such as atherosclerosis, heart failure, diabetes, hypertension, chronic kidney disease (CKD), and neurodegenerative diseases. The review summarizes traditional and novel potential biomarkers of endothelial dysfunction and pharmacological and nonpharmacological therapeutic strategies for its prevention and treatment. The review highlights the importance of understanding emerging biomarkers and therapeutic approaches to reduce the risk of CVD and its complications. Endothelial dysfunction is primarily caused by an imbalance between antioxidant defense mechanisms and reactive oxygen species (ROS) generation, leading to vascular damage. ROS and heightened oxidative stress play a crucial role in the development of endothelial dysfunction, as ROS serve as significant second messengers in cellular signaling. Inflammatory stimuli, including proinflammatory cytokines and cardiovascular risk factors, activate proinflammatory signaling pathways in endothelial cells (EC), leading to the upregulation of adhesion molecules. The main mechanisms of endothelial dysfunction involve impaired NO bioavailability and signaling pathways, oxidative stress, and inflammation-mediated pathways. NO is synthesized by three distinct subtypes of NO synthase (NOS) enzymes: inducible NOS (iNOS), endothelial NOS (eNOS), and neuronal NOS (nNOS). The production of NO occurs through the catalysis of L-arginine (L-Arg) and O₂ by NOS in EC, a process that necessitates the involvement of various cofactors. The NO-sGC-cGMP signaling pathway plays a crucial role in cardiovascular, renal, and metabolic functions. Endothelial dysfunction is also associated with oxidative stress, which can be mitigated by antioxidants and other therapeutic approaches. Inflammation-mediated pathways contribute to endothelial dysfunction by promoting the adhesion of monocytes and neutrophils to the walls of arteries. Endothelial dysfunction occurs due to perturbations in oxidative stress, inflammation, and pathophysiological shear stress, leading to a reduction in antithrombotic and anti-inflammatory functions, as well as degradation of the glycocalyx. The dysfunctional EC adopts a proinflammatory and prothrombotic phenotype, characterized by decreased production of prostacyclin and NO, and increased release of proinflammatory and prothrombotic molecules. Endothelial dysfunction is a significant contributor to multiple CVD and related complications. In heart failure (HF), endothelial dysfunction is associated with impaired vascular tone, myocardial remodeling, and abnormal cell proliferation. In atherosclerosis, endothelial dysfunction facilitates the infiltration of LDL into the subendothelial layer, leading to its accumulation and oxidation to ox-LDL. This process triggers the expression of cell adhesion