A method of phage-assisted continuous evolution, comprising (a) contacting a population of bacterial host cells with a population of M13 phages comprising a gene of interest to be evolved and lacking a full-length pIII gene or part of a pIII gene encoding a protein required for the generation of infectious phage particles, wherein the M13 phages allow for expression of the gene of interest in the host cells, the host cells are suitable host cells for M13 phage infection, replication, and packaging, wherein the M13 phage comprises all phage genes required for the generation of phage particles, except a full-length pIII gene or part of a pIII gene encoding a protein required for the generation of infectious phage particles; and the host cells comprise an expression construct encoding the pIII protein, wherein expression of the pIII gene from the expression construct is dependent on a function of a gene product of the gene of interest; (b) incubating the population of host cells under conditions allowing for the mutation of the gene of interest, the production of infectious M13 phage, and the infection of host cells with M13 phage, wherein infected cells are removed from the population of host cells, and wherein the population of host cells is replenished with fresh host cells that are not infected by M13 phage, wherein the function of the gene of interest is a desired function, wherein desired functional library members induce production of pIII and release M13 progeny into the culture medium capable of infecting new host cells, wherein undesired non-functional library members do not produce pIII and release only noninfectious M13 progeny into the culture medium; and (c) isolating a mutated M13 phage replication product encoding an evolved protein from the population of host cells, wherein the host cells comprise an expression construct encoding a dominant-negative pIII protein (pIII-neg), wherein expression of the pIII-neg protein is driven by a promoter the activity of which depends on an undesired function of a gene product encoded by the gene of interest. (a) contacting a population of bacterial host cells with a population of M13 phages comprising a gene of interest to be evolved and lacking a full-length pIII gene or part of a pIII gene encoding a protein required for the generation of infectious phage particles, wherein the M13 phages allow for expression of the gene of interest in the host cells, the host cells are suitable host cells for M13 phage infection, replication, and packaging, wherein the M13 phage comprises all phage genes required for the generation of phage particles, except a full-length pIII gene or part of a pIII gene encoding a protein required for the generation of infectious phage particles; and the host cells comprise an expression construct encoding the pIII protein, wherein expression of the pIII gene from the expression construct is dependent on a function of a gene product of the gene of interest; the M13 phages allow for expression of the gene of interest in the host cells, the host cells are suitable host cells for M13 phage infection, replication, and packaging, wherein the M13 phage comprises all phage genes required for the generation of phage particles, except a full-length pIII gene or part of a pIII gene encoding a protein required for the generation of infectious phage particles; and the host cells comprise an expression construct encoding the pIII protein, wherein expression of the pIII gene from the expression construct is dependent on a function of a gene product of the gene of interest; (b) incubating the population of host cells under conditions allowing for the mutation of the gene of interest, the production of infectious M13 phage, and the infection of host cells with M13 phage, wherein infected cells are removed from the population of host cells, and wherein the population of host cells is replenished with fresh host cells that are not infected by M13 phage, wherein the function of the gene of interest is a desired function, wherein desired functional library members induce production of pIII and release M13 progeny into the culture medium capable of infecting new host cells, wherein undesired non-functional library members do not produce pIII and release only noninfectious M13 progeny into the culture medium; and (c) isolating a mutated M13 phage replication product encoding an evolved protein from the population of host cells,