The party, which is not revealing details of strategy or spend, has hired Vizeum to handle its communications strategy, and media planning and buying.
The advertising is expected to build on the 10-point plan set out by party leader Charles Kennedy last month. It was backed by limited press advertising, under the strapline '10 good reasons to vote Liberal Democrat'.
The latest campaign, which will be created by Banc, is also intended to grab media attention and increase its share of both newspaper and TV coverage.
Liberal Democrats chief executive Lord Rennard said the party had identified a need to advertise its manifesto 'to raise the stakes and our profile'.
Separately, the Advertising Standards Authority said it has received 56 complaints about political ads this year, despite the fact it is not able to regulate them.
Brand health check, page 22
Leader, page 32.