A computer program comprising instructions which, when executed by one or more processors of a viewer-end computer, is arranged to perform a method of controlling and monitoring the rendering of electronic content to a viewer; wherein the computer program is such that, when executed by the viewer-end computer, a content rendering method is performed which comprises: requesting a content page to a system-end computer; receiving the content page from the system-end computer including written or embedded code, wherein the written or embedded code when executed by the viewer-end computer comprises: generating a link, to be stored as a variable within the content page requested by the viewer-end computer, generating a marker for a pre-defined area where designated content is to be rendered on the content page; correlating a pre-defined area with a browser window at the viewer-end computer by performing the steps of: determining whether the pre-defined area of the content page is within a pre-defined distance outside of the browser window dimensions and scrolling position; in response to determining that the pre-defined area is within the pre-defined distance outside of the browser window dimensions and scrolling position, causing the viewer-end computer to activate the link to request designated content from a content server and to receive and render the designated content within the pre-defined area of the content page. wherein the computer program is such that, when executed by the viewer-end computer, a content rendering method is performed which comprises: requesting a content page to a system-end computer; receiving the content page from the system-end computer including written or embedded code, wherein the written or embedded code when executed by the viewer-end computer comprises: generating a link, to be stored as a variable within the content page requested by the viewer-end computer, generating a marker for a pre-defined area where designated content is to be rendered on the content page; correlating a pre-defined area with a browser window at the viewer-end computer by performing the steps of: determining whether the pre-defined area of the content page is within a pre-defined distance outside of the browser window dimensions and scrolling position; in response to determining that the pre-defined area is within the pre-defined distance outside of the browser window dimensions and scrolling position, causing the viewer-end computer to activate the link to request designated content from a content server and to receive and render the designated content within the pre-defined area of the content page. requesting a content page to a system-end computer; receiving the content page from the system-end computer including written or embedded code, wherein the written or embedded code when executed by the viewer-end computer comprises: generating a link, to be stored as a variable within the content page requested by the viewer-end computer, generating a marker for a pre-defined area where designated content is to be rendered on the content page; correlating a pre-defined area with a browser window at the viewer-end computer by performing the steps of: determining whether the pre-defined area of the content page is within a pre-defined distance outside of the browser window dimensions and scrolling position; in response to determining that the pre-defined area is within the pre-defined distance outside of the browser window dimensions and scrolling position, causing the viewer-end computer to activate the link to request designated content from a content server and to receive and render the designated content within the pre-defined area of the content page. generating a link, to be stored as a variable within the content page requested by the viewer-end computer, generating a marker for a pre-defined area where designated content is to be rendered on the content page; correlating a pre-defined area with a browser window at the viewer-end computer by performing the steps of: determining whether the pre-defined area of the content page is within a pre-defined distance outside of the browser window dimensions and scrolling position; in response to determining that the pre-defined area is within the pre-defined distance outside of the browser window dimensions and scrolling position, causing the viewer-end computer to activate the link to request designated content from a content server and to receive and render the designated content within the pre-defined area of the content page. determining whether the pre-defined area of the content page is within a pre-defined distance outside of the browser window dimensions and scrolling position; in response to determining that the pre-defined area is within the pre-defined distance outside of the browser window dimensions and scrolling position, causing the viewer-end computer to activate the link to request designated content from a content server and to receive and render the designated content within the pre-defined area of the content page.