An overview will be given about the progress in mass spectrometer instrumentation throughout the last years using the five functional elements as a guideline: sample introduction, ion production, mass separation, ion current detection and instrument control/data handling. The relations between the functional elements will be discussed together with the physics behind these elements. Historical remarks and commentary related to instrumental development will also be presented. Introduction: Unique features of mass spectrometry. Reasons for their existence. Relation to optical spectrometry, Planck's and Einstein's laws. 1. 1. Sample Introduction: 1.1 Nonvolatiles: rapid heating/fast energy transfer, direct chemical ionization, particle bombardment (SIMS, FAB, laser, 252Cf), pyrolysis of biological samples. 1.2 On-Line: GC/MS- and LC/MS-interfacing, introduction and ionization of solids by inductively coupled plasma, on-line 13C/ 12C analyses of GC fractions. 1.3 Automation: automated direct probes, automated batch inlet systems. 1.4 Small samples: 13 C 12 C analyses, gas ion probe, automated introduction of thermionic samples. 2. 2. Ion Production: Why do mass spectrometers require ion sources? Gravity mass spectrometer. 3. 3. Mass Separation: 3.1 Transmission: basic ion optical laws, stigmatic and wide angle focusing, image error correction. 3.2 Speed: laminated magnets, fast and high resolution selected ion monitoring. 3.3 Specificity: various systems of MS/MS (sectors, quads), linked scan technique, multidimensional separation, selected ion flow tube, isotope separators, parabola spectrograph, secondary ion probe. 3.4 Mass range: high mass range sector instruments and quads, Wien-filter, time of flight instruments, Liouville's theorem. 3.5 Resolution: ion cyclotron/Fourier transform mass spectrometry, ultra-high resolution, ion trap, ultra-high precision mass determination. 4. 4. Ion Current Detection: Electro-optical ion detection, energetic ion mass spectrometer, multicollector systems, multichannel averaging, positive/negative ion detection, phase sensitive detection, coincidence photoion-photoelectron spectrometer. 5. 5. Instrument Control and Data Handling: Off-line processing/central computer, dedicated computer systems, fast data acquisition, instrument control through front end microprocessors, data-dependent experiments, lab data management, future aspects.