Lambda (λ) phage is the classic example of a head-and-tail bacteriophage (order Caudovirales). It has an icosahedral head containing double-stranded DNA and a flexible tail used for host recognition and DNA injection. Lambda phage infects E. coli and can follow either the lytic or lysogenic cycle. M13 is a filamentous (non-tailed) phage; pBR322 is a plasmid cloning vector, not a phage.