By many measures, this should be a moment of great economic uncertainty for the corporate world.

The United States election looms. Interest rates are set to rise soon. Britain plans to leave the European Union. China’s economic growth is slowing. Cyberattacks are on the rise. And Russia is flexing its military muscle in the Middle East.

Any one of these factors would usually be enough to give chief executives pause. The men and women who run the world’s largest corporations are nothing if not cautious.

Yet across industries, there are surprising signs of confidence, with corporate chieftains and directors signaling their belief that the upswing will continue for months or even years to come. Investors are betting on sustained growth. Companies are hiring. And huge mergers and acquisitions are back in fashion.

On Saturday night, AT&T said it planned to acquire Time Warner for $85.4 billion — the biggest deal of the year. On Friday, British American Tobacco offered $47 billion for the portion of Reynolds American that it does not already own. And this week, the chip maker Qualcomm is expected to make a $37 billion offer for the rival company NXP Semiconductors.