For laptop computers, the conventional internal antennas are usually used to operate in the WLAN system only, which can not provide sufficient and seamless services for wireless users. In order to overcome this problem, we propose some internal antennas having dual-/multi-network operation capability in this dissertation. Firstly, we present a combo antenna, which combines two shorted monopole antennas for operating in the WWAN/WLAN dual-network system. Secondly, we introduce a shorted monopole antenna through adding a parasitic element to enhance the impedance bandwidth for operating in the WLAN/WiMAX dual-network system. Thirdly, for achieving the compact-size antenna, we present a composite antenna which is composed of a ceramic chip and a printed radiating portion. Fourthly, we introduce a wideband shorted monopole antenna which can provide a wide bandwidth to cover the WPAN, WLAN, and WiMAX operations, and apply it to the MIMO system. Finally, we propose a coupling-type monopole antenna having multi-network operation capability and a compact size, which is about the smallest antenna for wideband operation in the laptop computer so far.