Share buyback will reduce the company's total number of shares outstanding and the total amount of cash on the company's balance sheet. In general, share buyback tends to increase the price of the stock not only due to the reduced supply of shares but also the buyback will boost earnings per share and drive down the price-to-earnings ratio, a key benchmark investors use to value a company. If the company has strong cashflow and its shares are undervalued, share buyback can be a good way to reward shareholders. With the US market $Dow Jones Industrial Average(.DJI.US)$, $Nasdaq Composite Index(.IXIC.US)$, $S&P 500 Index(.SPX.US)$ hitting record highs this year, share buyback by global giant companies  $Alphabet-A(GOOGL.US)$, $Apple(AAPL.US)$, $Bank of America(BAC.US)$ , $Facebook(FB.US)$,  $JPMorgan(JPM.US)$, $McDonald's(MCD.US)$, $Microsoft(MSFT.US)$, $Netflix(NFLX.US)$, often cited as a key support for US stocks could lift investor hopes by driving the market even higher. The main drivers of the share buyback are excess cash on balance sheets and positive sentiment on the back of healthy financial performance. While companies buying back their own shares can support higher stock prices , they run the risk of overvaluing stocks. Investors should proceed carefully if the buyback seems to be motivated by the management's desire to improve its valuation metrics rather than returning value to shareholders. Companies that use buyback to give the impression of rapid growth in earnings per share may not be worth investing in. Among the companies participating in share buyback, I am most bullish on $Apple(AAPL.US)$, one of Warren Buffett's all time favourite stocks. Its strong brand and innovative design expertise has allowed $Apple(AAPL.US)$ to build one of the most loyal customer bases in the world and generate earnings that beat its competitors in the mobile computing market. Not only that , $Apple(AAPL.US)$ has used its dominant position in mobile to build a largely profitable software ecosystem. Even better, $Apple(AAPL.US)$ pays consistently higher dividend and shareholders can anticipate a huge payout growth in the long term.