A very low-field emission was achieved from aligned and opened carbon nanotube arrays. Field emission current densities of 10 microamperes per square centimeter were observed at applied fields of 0.6-1 V/mum, and current densities of 10 mA/cm(2) have been realized at applied fields as low as 2-2.7 V/mum. These fields are more than 2 times lower than those previously obtained for carbon nanotubes, and also represent the lowest field ever reported for any field emitting arrays at the same current densities, indicating that carbon nanotubes are superior field emitters.