This invention features conjugates, degradable linkers, compositions, methods of synthesis, and applications thereof, including cholesterol, folate, galactose, galactosamine, N-acetyl galactosamine, PEG, phospholipid, peptide and human serum albumin (HSA) derived conjugates of biologically active compounds, including antibodies, antivirals, chemotherapeutics, peptides, proteins, hormones, nucleosides, nucleotides, non-nucleosides, and nucleic acids including enzymatic nucleic acids, DNAzymes, allozymes, antisense, dsRNA, siNA, siRNA, triplex oligonucleotides, 2,5-A chimeras, decoys and aptamers.