What is the name of Pokemon Sinnoh theme song?

The main theme song for Pokemon Diamond and Pearl (Sinnoh region) is called "Pokémon - Diamond & Pearl Opening Theme" or simply "Diamond & Pearl Opening Theme". It's a catchy, upbeat song that uses a lot of brass instruments and a strong piano melody.

It's the theme song that plays at the beginning of the anime series and is featured in the games' title screen.