Among other things, the present disclosure provides designed oligonucleotides, compositions, and methods thereof. In some embodiments, provided oligonucleotide compositions provide improved single-stranded RNA interference and/or RNase H-mediated knockdown. Among other things, the present disclosure encompasses the recognition that structural elements of oligonucleotides, such as base sequence, chemical modifications (e.g., modifications of sugar, base, and/or internucleotidic linkages) or patterns thereof, conjugation with additional chemical moieties, and/or stereochemistry [e.g., stereochemistry of backbone chiral centers (chiral internucleotidic linkages)], and/or patterns thereof, can have significant impact on oligonucleotide properties and activities, e.g., RNA interference (RNAi) activity, stability, delivery, etc. In some embodiments, the present disclosure provides methods for treatment of diseases using provided oligonucleotide compositions, for example, in RNA interference and/or RNase H-mediated knockdown.