The <a href="https://en.wikipedia.org/wiki/Treaty_of_Lisbon" id="mwATs" rel="mw:WikiLink" title="Treaty of Lisbon">Treaty of Lisbon</a> is signed by the <a href="https://en.wikipedia.org/wiki/Member_state_of_the_European_Union" id="mwATw" rel="mw:WikiLink" title="Member state of the European Union">EU member states</a> to amend both the <a href="https://en.wikipedia.org/wiki/Treaty_of_Rome" id="mwAT0" rel="mw:WikiLink" title="Treaty of Rome">Treaty of Rome</a> and the <a href="https://en.wikipedia.org/wiki/Maastricht_Treaty" id="mwAT4" rel="mw:WikiLink" title="Maastricht Treaty">Maastricht Treaty</a> which together form the constitutional basis of the EU. The Treaty of Lisbon is effective from 1 December 2009.<sup about="#mwt111" class="mw-ref reference" data-mw='{"name":"ref","attrs":{},"body":{"id":"mw-reference-text-cite_note-19"}}' id="cite_ref-19" rel="dc:references" typeof="mw:Extension/ref"><a href="./December_13#cite_note-19" id="mwAT8" style="counter-reset: mw-Ref 19;"><span class="mw-reflink-text" id="mwAUA">[19]</span></a></sup>
<span class="mw-reference-text reference-text" id="mw-reference-text-cite_note-19"><cite about="#mwt108" class="citation web cs1" id="mwBkY"><a class="external text" href="https://www.europarl.europa.eu/factsheets/en/sheet/5/the-treaty-of-lisbon" id="mwBkc" rel="mw:ExtLink nofollow">"The Treaty of Lisbon"</a>. Fact Sheets on the European Union. Brussels: European Parliament<span class="reference-accessdate" id="mwBkg">. Retrieved <span class="nowrap" id="mwBkk">16 January</span> 2021</span>.</cite><span about="#mwt108" class="Z3988" id="mwBko" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&amp;rft.genre=unknown&amp;rft.btitle=The+Treaty+of+Lisbon&amp;rft.place=Brussels&amp;rft.series=Fact+Sheets+on+the+European+Union&amp;rft.pub=European+Parliament&amp;rft_id=https%3A%2F%2Fwww.europarl.europa.eu%2Ffactsheets%2Fen%2Fsheet%2F5%2Fthe-treaty-of-lisbon&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3ADecember+13"></span></span>