Self-assembled nanoreactors are confined environments that mimic cellular processes, enabling controlled chemical reactions. This review discusses various types of nanoreactors, including molecular, macromolecular, and biomacromolecular systems, constructed using both covalent and noncovalent approaches. The focus is on self-assembled systems ranging from a few nanometers to tens of micrometers. These systems can act as catalysts, stabilizing reactive intermediates or enhancing reaction efficiency and selectivity. Molecular nanoreactors include capsules and boxes, such as covalent systems like cyclodextrins and noncovalent systems like cucurbituril. These systems can catalyze reactions by encapsulating substrates and positioning them for efficient conversion. For example, cucurbituril catalyzes the 1,3-dipolar cycloaddition of propargylammonium and azidoethylammonium, significantly increasing reaction rates and selectivity. Macromolecular nanoreactors, such as polymersomes and polymer micelles, offer larger, more complex structures for reactions. These systems can encapsulate multiple substrates and promote reactions between them, enhancing selectivity and efficiency. For instance, a polymer micelle can act as a confined environment for the Diels–Alder reaction, increasing the rate and favoring specific isomers. Biomacromolecular nanoreactors, such as protein cages and viruses, utilize natural structures to perform reactions. For example, ferritin and viral capsids can encapsulate substrates and catalyze reactions, offering high selectivity and stability. Viruses, such as rod-shaped and cage-structured viruses, have been explored as nanocontainers for reactions, demonstrating their potential in catalysis and drug delivery. The review highlights the importance of self-assembly in creating nanoreactors with controlled environments, enabling efficient and selective chemical transformations. These systems have applications in catalysis, drug delivery, and synthetic chemistry, offering a promising approach to mimic natural processes in controlled environments.Self-assembled nanoreactors are confined environments that mimic cellular processes, enabling controlled chemical reactions. This review discusses various types of nanoreactors, including molecular, macromolecular, and biomacromolecular systems, constructed using both covalent and noncovalent approaches. The focus is on self-assembled systems ranging from a few nanometers to tens of micrometers. These systems can act as catalysts, stabilizing reactive intermediates or enhancing reaction efficiency and selectivity. Molecular nanoreactors include capsules and boxes, such as covalent systems like cyclodextrins and noncovalent systems like cucurbituril. These systems can catalyze reactions by encapsulating substrates and positioning them for efficient conversion. For example, cucurbituril catalyzes the 1,3-dipolar cycloaddition of propargylammonium and azidoethylammonium, significantly increasing reaction rates and selectivity. Macromolecular nanoreactors, such as polymersomes and polymer micelles, offer larger, more complex structures for reactions. These systems can encapsulate multiple substrates and promote reactions between them, enhancing selectivity and efficiency. For instance, a polymer micelle can act as a confined environment for the Diels–Alder reaction, increasing the rate and favoring specific isomers. Biomacromolecular nanoreactors, such as protein cages and viruses, utilize natural structures to perform reactions. For example, ferritin and viral capsids can encapsulate substrates and catalyze reactions, offering high selectivity and stability. Viruses, such as rod-shaped and cage-structured viruses, have been explored as nanocontainers for reactions, demonstrating their potential in catalysis and drug delivery. The review highlights the importance of self-assembly in creating nanoreactors with controlled environments, enabling efficient and selective chemical transformations. These systems have applications in catalysis, drug delivery, and synthetic chemistry, offering a promising approach to mimic natural processes in controlled environments.