Polymeric nanoparticles (NPs) have shown potential in improving disease therapies due to their ability to overcome biological barriers and deliver drugs in optimal dosages. However, rapid clearance during systemic delivery is a critical issue, necessitating understanding of factors affecting their biodistribution and blood circulation half-life. This review discusses factors influencing NP blood residence time and organ-specific accumulation, including interactions with biological barriers, tunable NP parameters such as composition, size, core properties, surface modifications (pegylation and surface charge), and targeting ligand functionalization. These factors significantly affect NP biodistribution and circulation half-life by reducing nonspecific uptake, delaying opsonization, and increasing tissue-specific accumulation. NPs must overcome biological barriers, including the immune system and mucosal barriers, to reach their target. Their unique size and surface functionalization capabilities make them well-suited for this task. Abnormal neovascularization, such as in tumors, leads to defective hypervasculature and lymphatic drainage, enabling the "enhanced permeability and retention" (EPR) effect, which allows macromolecules and NPs to accumulate in tumor tissues. NPs with stealth properties, such as PEGylation, reduce protein adsorption and opsonization, enhancing circulation time and targeting. Nanoparticle composition, size, and surface properties significantly affect biodistribution. PEGylation reduces plasma protein adsorption and opsonization, increasing circulation time and tumor accumulation. Smaller NPs (<100 nm) have reduced hepatic filtration and longer blood residence times. The core composition also influences biodistribution; for example, PCL-based NPs have longer blood residence times compared to PLA-based NPs. Surface functionality and charge are critical; neutral or negatively charged NPs have reduced plasma protein adsorption and lower nonspecific uptake. Active targeting using ligands such as antibodies or peptides enhances NP accumulation in specific tissues or cells. Immunoconjugates, which combine targeting specificity with potent drugs, have shown promise in clinical applications. However, challenges remain in their development. Overall, understanding and optimizing NP properties are essential for effective, targeted drug delivery.Polymeric nanoparticles (NPs) have shown potential in improving disease therapies due to their ability to overcome biological barriers and deliver drugs in optimal dosages. However, rapid clearance during systemic delivery is a critical issue, necessitating understanding of factors affecting their biodistribution and blood circulation half-life. This review discusses factors influencing NP blood residence time and organ-specific accumulation, including interactions with biological barriers, tunable NP parameters such as composition, size, core properties, surface modifications (pegylation and surface charge), and targeting ligand functionalization. These factors significantly affect NP biodistribution and circulation half-life by reducing nonspecific uptake, delaying opsonization, and increasing tissue-specific accumulation. NPs must overcome biological barriers, including the immune system and mucosal barriers, to reach their target. Their unique size and surface functionalization capabilities make them well-suited for this task. Abnormal neovascularization, such as in tumors, leads to defective hypervasculature and lymphatic drainage, enabling the "enhanced permeability and retention" (EPR) effect, which allows macromolecules and NPs to accumulate in tumor tissues. NPs with stealth properties, such as PEGylation, reduce protein adsorption and opsonization, enhancing circulation time and targeting. Nanoparticle composition, size, and surface properties significantly affect biodistribution. PEGylation reduces plasma protein adsorption and opsonization, increasing circulation time and tumor accumulation. Smaller NPs (<100 nm) have reduced hepatic filtration and longer blood residence times. The core composition also influences biodistribution; for example, PCL-based NPs have longer blood residence times compared to PLA-based NPs. Surface functionality and charge are critical; neutral or negatively charged NPs have reduced plasma protein adsorption and lower nonspecific uptake. Active targeting using ligands such as antibodies or peptides enhances NP accumulation in specific tissues or cells. Immunoconjugates, which combine targeting specificity with potent drugs, have shown promise in clinical applications. However, challenges remain in their development. Overall, understanding and optimizing NP properties are essential for effective, targeted drug delivery.