A process for producing recombinant adeno-associated virus particles, the process comprising the steps: (a) culturing a population of first host cells, wherein each first host cell comprises: (i) a nucleic acid molecule encoding a recombinant AAV genome; (ii) a nucleic acid molecule encoding a first AAV cap gene which encodes first AAV capsid polypeptides, wherein the first AAV capsid polypeptides confer a tropism on AAV particles which comprise such polypeptides towards second host cells; (iii) a nucleic acid molecule encoding an AAV rep gene; (iv) nucleic acid molecules encoding viral helper genes; such that the expression of each of (i)-(iv) in the first host cells is sufficient to produce first recombinant AAV particles comprising the AAV genome in the first host cells, wherein the first AAV particles are encapsidated by first AAV capsid polypeptides; (b) infecting a population of second host cells with the first recombinant AAV particles which are produced from Step (a); (c) expressing in the population of second host cells: (i) a nucleic acid molecule encoding a second AAV cap gene which encodes second AAV capsid polypeptides, wherein the second AAV capsid polypeptides confer a tropism on AAV particles which comprise such polypeptides towards third host cells; (ii) a nucleic acid molecule encoding an AAV rep gene; (iii) nucleic acid molecules encoding viral helper genes; wherein all of (i)-(iii) are independently either present in the second host cells or are subsequently introduced into the second host cells, such that the expression of each of (i)-(iii) in the second cells is sufficient to produce second recombinant AAV particles comprising the recombinant AAV genome in the second host cells, wherein the second recombinant AAV particles are encapsidated by the second AAV capsid polypeptides; (d) culturing the second host cells in a culture medium under conditions such that second recombinant AAV particles comprising the recombinant AAV genome are produced, the second recombinant AAV particles each being encapsidated by a capsid comprising the second capsid polypeptides; and optionally, (e) purifying and/or isolating second recombinant AAV particles from the second host cells or from the culture medium. (a) culturing a population of first host cells, wherein each first host cell comprises: (i) a nucleic acid molecule encoding a recombinant AAV genome; (ii) a nucleic acid molecule encoding a first AAV cap gene which encodes first AAV capsid polypeptides, wherein the first AAV capsid polypeptides confer a tropism on AAV particles which comprise such polypeptides towards second host cells; (iii) a nucleic acid molecule encoding an AAV rep gene; (iv) nucleic acid molecules encoding viral helper genes; such that the expression of each of (i)-(iv) in the first host cells is sufficient to produce first recombinant AAV particles comprising the AAV genome in the first host cells, wherein the first AAV particles are encapsidated by first AAV capsid polypeptides; (i) a nucleic acid molecule encoding a recombinant AAV genome; (ii) a nucleic acid molecule encoding a first AAV cap gene which encodes first AAV capsid polypeptides, wherein the first AAV capsid polypeptides confer a tropism on AAV particles which comprise such polypeptides towards second host cells; (iii) a nucleic acid molecule encoding an AAV rep gene; (iv) nucleic acid molecules encoding viral helper genes; (b) infecting a population of second host cells with the first recombinant AAV particles which are produced from Step (a); (c) expressing in the population of second host cells: (i) a nucleic acid molecule encoding a second AAV cap gene which encodes second AAV capsid polypeptides, wherein the second AAV capsid polypeptides confer a tropism on AAV particles which comprise such polypeptides towards third host cells; (ii) a nucleic acid molecule encoding an AAV rep gene; (iii) nucleic acid molecules encoding viral helper genes; wherein all of (i)-(iii) are independently either present in the second host cells or are subsequently introduced into the second host cells, such that the expression of each of (i)-(iii) in the second cells is sufficient to produce second recombinant AAV particles comprising the recombinant AAV genome in the second host cells, wherein the second recombinant AAV particles are encapsidated by the second AAV capsid polypeptides; (i) a nucleic acid molecule encoding a second AAV cap gene which encodes second AAV capsid polypeptides, wherein the second AAV capsid polypeptides confer a tropism on AAV particles which comprise such polypeptides towards third host cells; (ii) a nucleic acid molecule encoding an AAV rep gene; (iii) nucleic acid molecules encoding viral helper genes; wherein all of (i)-(iii) are independently either present in the second host cells or are subsequently introduced into the second host cells, such that the expression of each of (i)-(iii) in the second cells is sufficient to produce second recombinant AAV particles comprising the recombinant AAV genome in the second host cells, wherein the second recombinant AAV particles are encapsidated by the second AAV capsid polypeptides; (d) culturing the second host cells in a culture medium under conditions such that second recombinant AAV particles comprising the recombinant AAV genome are produced, the second recombinant AAV particles each being encapsidated by a capsid comprising the second capsid polypeptides; and optionally, (e) purifying and/or isolating second recombinant AAV particles from the second host cells or from the culture medium.