The present invention relates to chirally controlled oligonucleotides, chirally controlled oligonucleotide compositions, and the method of making and using the same. The invention specifically encompasses the identification of the source of certain problems with prior methodologies for preparing chiral oligonucleotides, including problems that prohibit preparation of fully chirally controlled compositions, particularly compositions comprising a plurality of oligonucleotide types. In some embodiments, the present invention provides chirally controlled oligonucleotide compositions. In some embodiments, the present invention provides methods of making chirally controlled oligonucleotides and chirally controlled oligonucleotide compositions.
