The article introduces CLUSTAL V, an improved version of the CLUSTAL package for multiple sequence alignment. CLUSTAL V is a single program written in C, making it portable to various operating systems. Key features include the ability to store and reuse old alignments, calculate phylogenetic trees with bootstrap confidence intervals, and align old alignments with each other. The program is menu-driven, user-friendly, and supports flexible sequence input and output formats. It can handle large sequences and multiple alignments efficiently, using a progressive alignment strategy. CLUSTAL V also offers phylogenetic tree calculations using the Neighbor-Joining method and confidence intervals through bootstrapping. The program is available from the EMBL file server, and the authors provide contact information for support and inquiries.The article introduces CLUSTAL V, an improved version of the CLUSTAL package for multiple sequence alignment. CLUSTAL V is a single program written in C, making it portable to various operating systems. Key features include the ability to store and reuse old alignments, calculate phylogenetic trees with bootstrap confidence intervals, and align old alignments with each other. The program is menu-driven, user-friendly, and supports flexible sequence input and output formats. It can handle large sequences and multiple alignments efficiently, using a progressive alignment strategy. CLUSTAL V also offers phylogenetic tree calculations using the Neighbor-Joining method and confidence intervals through bootstrapping. The program is available from the EMBL file server, and the authors provide contact information for support and inquiries.