A tender offer is a public bid for a large chunk of the target's stock at a fixed price, usually higher than the current market value of the stock. The purchaser uses a premium price to encourage the shareholders to sell their shares. The offer has a time limit, and it may have other provisions that the target company must abide by if shareholders accept the offer. The bidding company must disclose their plans for the target company and file the proper documents with the Securities and Exchange Commission (SEC). The 1966 Williams Act put restrictions and provisions on tender offers.

Sometimes, a purchaser or group of purchasers will gradually buy up enough stock to gain a controlling interest (known as a creeping tender offer), without making a public tender offer. This bypasses the Williams Act, but is risky because the target company could discover the takeover and take steps to prevent it.

In a proxy fight, the buyer doesn't attempt to buy stock. Instead, they try to convince the shareholders to vote out current management or the current board of directors in favor of a team that will approve the takeover. The term "proxy" refers to the shareholders' ability to let someone else make their vote for them -- the buyer votes for the new board by proxy.

Often, a proxy fight originates within the company itself. A group of disgruntled shareholders or even managers might seek a change in ownership, so they try to convince other shareholders to band together. The proxy fight is popular because it bypasses many of the defenses that companies put into place to prevent takeovers. Most of those defenses are designed to prevent takeover by purchase of a controlling interest of stock, which the proxy fight sidesteps by changing the opinions of the people who already own it.

The most famous recent proxy fight was Hewlett-Packard's takeover of Compaq. The deal was valued at $25 billion, but Hewlett-Packard reportedly spent huge sums on advertising to sway shareholders [ref]. HP wasn't fighting Compaq -- they were fighting a group of investors that included founding members of the company who opposed the merge. About 51 percent of shareholders voted in favor of the merger. Despite attempts to halt the deal on legal grounds, it went as planned.