Below you will find links to essential CCSS documents--everything you ever wanted to know about the Common Core and more.
CCSS for Mathematics
The Standards, by grade level.
The Mathematical Practices
Detailed explanations with examples of the 8 Standards for Mathematical Practice.
The Mathematics Framework Chapters (by grade level)
From the California Department of Education.
Progressions for Mathematics
Excellent resource to look at coherence of concepts across grade levels.