Embodiments of abrasive jet piercing and/or cutting devices are described herein. In some embodiments, a piercing device includes a holding or positioning device coupling a mixing tube to a secondary tube. The holding device has one or more passages extending to at least an intermediate portion of the piercing device. The one or more passages allow air to contact or mix with an abrasive waterjet as it travels through the piercing device. In some embodiments, a cutting device includes two plates configured so as to form a slot between the two plates. The cutting device can be placed directly on a workpiece, and an abrasive waterjet can be directed at the workpiece through the slot. An abrasive waterjet system utilizing the piercing and cutting devices disclosed herein can pierce holes and cut slots in materials that have reduced hole diameters and kerf widths, respectively.