BBC News
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image captionAdam Price announced the party will use the slogan "Vote for Wales"
Plaid Cymru's leader has vowed to "harness the spirit" of the party's strong performance in the 1999 assembly election in next May's Senedd poll.
Adam Price said his party would invoke "the spirit of optimism, of hope, of a new beginning with a new government".
All Welsh Governments have been led by Labour, sometimes in coalition with Liberal Democrats or Plaid Cymru.
In 1999, Plaid won 17 of the 60 seats, some in traditional Labour heartlands such as the south Wales valleys.
Plaid Cymru came second at the last devolved poll in 2016, winning 12 seats in Cardiff Bay, but it now has 10 after Lord Elis-Thomas quit the party and Neil McEvoy was expelled.