Reactions of gas-phase species with small molecules are being actively studied to understand the elementary steps and mechanistic details of related condensed-phase processes. Activation of the very inert N$\equiv$N triple bond of dinitrogen molecule by isolated gas-phase species has attracted considerable interest in the past few decades. Apart from molecular adsorption and dissociative adsorption, interesting processes such as C-N coupling and degenerate ligand exchange were discovered. The present review focuses on the recent progress on adsorption, activation, and functionalization of N₂ by gas-phase species (particularly metal cluster ions) using mass spectrometry, infrared photo-dissociation spectroscopy, anion photoelectron spectroscopy, and quantum chemical calculations including density functional theory and high-level ab initio calculations. Recent advances including characterization of adsorption products, dependence of clusters' reactivity on their sizes and structures, and mechanisms of N$\equiv$N weakening and splitting have been emphasized and prospects have been discussed.