From the  New York Times

"Allergan agree to $150 billion merger

Pfizer and Allergan have reached a $150 million merger deal in one of the largest ever acquisitions in the health care industry. The boards of the two companies reportedly approved the deal on Sunday. The deal will likely be announced on Monday, according to sources. People briefed on the deal say that although Pfizer is much larger, with a market value of about $199 billion compared with Allergan's $123 billion, Allergan would be the technical buyer. Allergan's headquarters are in Dublin—though most of its operations are in Parsippany, NJ—the planned merger would avoid new Treasury Department and Internal Revenue Service rules on corporate inversions. The new rules, which apply to American companies that acquire foreign firms, are meant to further crack down on the billions of dollars in corporate tax revenue lost from such deals. In adopting Ireland as its home base, Pfizer—whose tax rate last year was about 26.5%—would see significant savings. Pfizer would lead the merged company in most cases, and its CEO, Ian Read, will take the helm of the combined firm, according to sources."