Some embodiments include constructions which have platinum-containing structures. In some embodiments, the constructions may have a planarized surface extending across the platinum-containing structures and across metal oxide. In some embodiments, the constructions may have a planarized surface extending across the platinum-containing structures, across a first material retaining the platinum-containing structures, and across metal oxide liners along sidewalls of the platinum-containing structures and directly between the platinum-containing structures and the first material. Some embodiments include methods of forming platinum-containing structures. In some embodiments, first material is formed across electrically conductive structures, and metal oxide is formed across the first material. Openings are formed to extend through the metal oxide and the first material to the electrically conductive structures. Platinum-containing material is formed within the openings and over the metal oxide. Chemical-mechanical polishing is utilized to form a planarized surface extending across the platinum-containing material and the metal oxide.