The delivery of nucleic acids (DNA/RNA) into cells is of utmost importance for gene expression and silencing experiments and requires an adequate transfection strategy. Several ways for a successful transfection have been identified. One method is based on the complexation of cationic polymers with the negatively charged DNA/RNA molecules. By adhesion to the cell membrane and subsequent endocytosis, the complex is taken up by the cells. Reagents that can be used in this manner are DEAE- dextran or polyethylenimine. Another strategy is the principle of receptor-mediated internalization. Such receptor ligands like Folate-PEG3-Azide show outstanding transfection properties. Choosing the right transfection reagent is very important and should be considered for each cell type.