Covalently lipidated oligonucleotides comprising the CpG dinucleotide unit, or an analogue thereof, may be used as immunostimulatory agents to protect against a disease caused by a cancer cell or a pathogen, either alone or in conjunction with immunogens and/or non-immunological agents.Lipidated oligonucleotides with special backbones, lipidated oligonucleotides with fewer than eight nucleotides, and lipidated oligonucleotides comprising a plurality of CpG dinucleotide-containing segments connected by a long internucleoside linkage are of particular interest. These compounds are also novel per se.