Under U.S. immigration law, there are certain relatives that U.S. citizens are allowed to petition for permanent resident status for. Brothers and sisters are included among the family members citizens can sponsor for a green card. As a note, a citizen has to be at least 21 to petition for a green card for a sibling.
The siblings U.S. citizens are allowed to sponsor are not limited to just full biological siblings. Citizens also, generally, can petition for permanent resident status for half-siblings, step-siblings and adoptive siblings.
There are a variety of documents U.S. citizens are required to provide when petitioning for a green card for a brother or sister. Among the standard required documents are Form I-130, evidence of U.S. citizenship, and a copy of the foreign national's birth certificate. An important thing to note is that, if the U.S. citizen sibling is petitioning for a paternal half-sibling (biologically related solely through a shared father), step-sibling or a sibling through adoption, there are additional types of documentation that are asked for on top of the standard ones.
Carefully meeting all applicable documentation requirements is very important for a U.S. citizen when petitioning for permanent resident status for a sibling or other qualifying relative. Documentation-related mistakes or oversights could get in the way of a petition succeeding. Immigration lawyers can provide U.S. citizens who desire to pursue a green card for a sibling or other relative with guidance on what the documentation requirements would be for the petitioning process given their particular situation and what steps can help with avoiding documentation-related mistakes.
Source: U.S. Citizenship and Immigration Services, "Bringing Siblings to Live in the United States as Permanent Residents," Accessed Jan. 5, 2016