The chemical reactivity is one of the leading properties for practically all-usual application of glass. Besides the published ideas and theories concerning the chemical interaction of glasses with different substances and materials, the concept of pB - oxide basicity – offers a new possibility of discussing and interpreting this property. The glass composition and structure may be considered by means of a single figure representing the basicity. This comprehensive magnitude correlates with all glass properties and has a decisive role in chemical interactions too. The ideas and data presented in this work illustrate the above affirmations and the fact that basicity is a powerful tool for oxide reactivity understanding.