(A) HIV infects susceptible cells, and reverse transcription takes place early after infection, following attachment and fusion. Both RNA copies are required for replication, and multiple strand transfers between the two molecules occur, resulting in frequent recombination. The terminal repeats are duplicated at each end of the integration, and the product of reverse transcription is a full-length molecule containing LTRs. As a consequence of complex interactions and strand transfers, defective copies with large internal deletions (but intact 5′ and 3′ ends) are frequent products of reverse transcription. Reverse transcripts with HIV Gag p24 and IN compose the viral PIC, which is transported to the nucleus, a process requiring specific host proteins, including nucleoporins. In the nucleus, PIC structures interact with host protein LEDGF/p75, which preferentially facilitates integration in areas of transcriptional activity. (B) IN is a dimer of dimers that creates 5-bp staggered cuts in each DNA strand of the integration site, resulting in a 5-nt duplication of the host sequence for each integrant. Integration is completed by host enzymes, which fill in the staggered cuts. Integration sites are frequently mutated or internally deleted, but have precise integration sites with duplications of the host sequence at each end of the provirus. (C) Not all of the newly synthesized viral DNA molecules are integrated into the host genome; a subset of DNA molecules form circular molecules that include one or both LTRs (1- and 2-LTR circles).