SEATTLE — Microsoft is trying to shake the effects of middle age.

The company, which is now 39 years old, said on Thursday that it was laying off up to 18,000 employees, in an attempt at reinvigoration. The cuts are the first major change made by Satya Nadella, the company’s new chief executive, who said Microsoft needed to be more nimble and focused.

The job cuts would be the largest in the company’s history, representing about 14 percent of its work force. Most of the cuts will come from the Nokia mobile phone business Microsoft acquired this year.

While Microsoft still makes profits that executives at other companies would be ecstatic to have, it has been beaten on the biggest new trends in tech, including mobile, Internet search and cloud computing. As a result, it is regularly left out of conversations about companies defining the next generation of technology, outflanked and overshadowed by companies like Apple, Google, Facebook and Amazon.

Cutting jobs does not mean the company will suddenly begin creating products that people love. And the cuts did not suggest a sharp shift in strategy. But it is a start of something new, in the view of many Microsoft critics, and one that could help the company concentrate on the businesses where it is likely to have the most impact.