The mean interference effects between two and among three tall buildings are studied by a series of wind tunnel tests. Both the shielding and channeling effects are discussed to understand the complexity of the multiple-building effects. The results show that the upstream interfering buildings cause certain shielding effect by decreasing the mean wind load on the downstream principal building. For buildings of the same height, the shielding effect increases and, therefore, the interference factor (IF) decreases, with the increase of the breadth of the interfering buildings. However, due to the channeling effects, two adjacent interfering buildings can significantly enhance the mean wind load on the principal building. In addition, the variation of the shielding effect is found to be significant when the heights of interfering buildings range from 50% to 125% of the height of the principal building. However, higher interfering buildings may cause stronger channeling effects.