Following Serbia's application for EU membership, the Commission will also present in the 2011 package its Opinion on the readiness of Serbia to start accession negotiations. In this document, the Commission offers a detailed analysis in reference to the Copenhagen criteria for membership and recommends next steps to member states. The Opinion replaced this year's progress report on Serbia.
Following the closure of accession negotiations with Croatia, the Commission will also present a formal opinion in line with Article 49 TEU confirming Croatia's readiness to sign an accession treaty with the EU.

The Commission has been mandated by the member states to report annually on progress achieved by all candidates and potential candidates. This monitoring process ensures that aspiring countries are admitted only when they have met all requirements. The conditions and concrete requirements for accession have been spelled out to all the countries wishing to join. Concerning Serbia, the Council has mandated the Commission to provide its Opinion on the country's membership application. This is presented as part of the present enlargement package.

What will be the consequence of these reports?
The Commission's strategy paper, as well as the Opinion on Serbia, will provide the basis for a debate among the member states in the Council. The European Council will decide unanimously in their meeting in December 2011 about possible next steps for any country moving towards EU membership on the basis of each of the countries' own merits. Meanwhile, the countries in question will receive a clear indication of the current state of play regarding their efforts to pursue a European path. The Commission will continue to help the countries implement the necessary reforms.

Source: http://ec.europa.eu/enlargement/pdf/key_documents/2011/package/citizens_summary_2011_en.pdf