Application systems for use with medical devices

An application or an attachment device for attaching a medical device includes a base layer and an adhesive layer on a rearward side of the base layer. The adhesive layer is adapted to removably attach the base layer. The adhesive layer can be adapted to removably attach the base layer to a patient (either a human patient or a lower animal patient). The device also includes a medical device attachment mechanism on a forward side of the base layer, The attachment mechanism is adapted to attach the medical device to the base layer. The medical device can, for example, be a sensor. The medical device attachment mechanism can, for example, include a mechanical attachment mechanism. The medical device attachment mechanism can additionally or alternatively include at least one adhesive layer on the base layer. The adhesive layer can, for example, be positioned on the base layer so that it does not extend beyond a footprint of the medical device when the medical device is attached to the base layer.