Based on the extremely popular   Koren Sacks Siddur , the   Koren Shalem Siddur   is a new, enhanced siddur that includes the entire contents of the Sacks Siddur AND:  

All Torah readings with new translations for the Shalosh Regalim and Hol HaMoed, Hanukka, Purim, Yom Ha'atzmaut and Yom Yerushalayim.
Modern English translations of the Five Megillot.
Additional personal supplications (tehinot)

For ease of use, and to facilitate adoption in synagogues and schools, the  Koren Shalem Siddur  maintains the same pagination as the  Koren Sacks Siddur