SEM是Search Engine Marketing的縮寫，意思為搜尋引擎营銷，是一種以透過增加搜尋引擎結果頁（Search Engine Result Pages，SERP）或內容聯播網的能見度來推廣網站流量，以增加產品或服務的營業額。目前市場上主流的SEM為關鍵字點擊廣告（PPC）如Google Adwords 關鍵字廣告以及付費收錄廣告（PFI）。搜尋引擎行銷是透過用家自發性的行為，有別於傳統的強迫曝光的橫幅廣告(Banner)，所以SEM是目前網路行銷方式中點閱率相當高的一種行銷方式。
由於 SEM每個點擊都需要付費，客戶會希望廣告投放得精準，務求每個點擊的搜尋用戶是都是潛在客戶以達成銷售，否則就徒然浪費金錢。廣告要投得精準，需要在關鍵詞、投放時間、目標客戶、文案質素、關聯性各方面調研測試。所以要SEM做得好確實需要相當的專業經驗和大量時間去營運管理，因而不少企業會聘用SEM行銷公司以達最佳的關鍵字廣告效果。
SEM is the abbreviation of Search Engine Marketing. It is to increase the sales of products or services by increasing the visibility of the website via the Search Engine Result Pages (SERP) or the display content network. Mainstream SEMs in the market are Pay Per click ads (PPC) such as Google Adwords keyword ads and paid inclusion ads (PFI). Search engine marketing is a banner advertisement that is different from the traditional exposure through the spontaneous behavior of the user. Therefore, SEM is a marketing method with a high click rate in the online marketing.
Since each SEM click subjects to fee charge, advertisement has to be accurately placed, so that each of the clicks are potential customers. The accuracy of the advertisement placement requires research and testing in terms of keywords, time of delivery, target audience, quality of copywriting, and relevancy. Therefore, to do a good job in SEM does require considerable professional experience and a lot of time in campaign management; to achieve cost effective keyword advertising results.
