A recombinant lentiviral vector expression system comprises a first vector that comprises a nucleic acid sequence of at least part of the Equine Infectious Anemia Virus (EIAV) genome. The vector contains at least one defect in at least one gene encoding an EIAV structural protein, but is preferably a gaglpol expression vector. The expression system further comprises a second vector, also comprising a nucleic acid sequence of at least part of the Equine Infectious Anemia Virus (EIAV) genome, and additionally containing a multiple cloning site wherein a heterologous gene may be inserted. The expression system also comprises a third vector which expresses a viral envelope protein. The first and third vectors are packaging signal-defective. When the expression system is transfected into a lentivirus-permissive cell, replication-defective EIAV particles may be produced, which particles are useful in delivering heterologous genes to a broad range of both dividing and non-dividing cells.