Amine alkylation (amino-dehalogenation) is a type of organic reaction between an alkyl halide and ammonia or an amine. The reaction is called nucleophilic aliphatic substitution (of the halide), and the reaction product is a higher substituted amine.  The method is widely used in the laboratory, but less so industrially, where alcohols are often preferred alkylating agents.
When the amine is a tertiary amine the reaction product is a quaternary ammonium salt in the Menshutkin reaction:
Amines and ammonia are generally sufficiently nucleophilic to undergo direct alkylation, often under mild conditions.  The reactions are complicated by the tendency of the product (a primary amine or a secondary amine) to react with the alkylating agent. For example, reaction of 1-bromooctane with ammonia yields almost equal amounts of the primary amine and the secondary amine.  Therefore, for laboratory purposes, N-alkylation is often limited to the synthesis of tertiary amines. An exception is the amination of alpha-halo carboxylic acids that do permit synthesis of primary amines with ammonia. Intramolecular reactions of haloamines X-(CH)-NH give cyclic aziridines,  azetidines and pyrrolidines.
N-alkylation is a general and useful route to quaternary ammonium salts from tertiary amines, because overalkylation is not possible.
Examples of N-alkylation with alkyl halides are the syntheses of benzylaniline, 1-benzylindole, and azetidine. Another example is found in the derivatization of cyclen.  Industrially, ethylenediamine is produced by alkylation of ammonia with 1,2-dichloroethane.