Capacitors are mainly classified into the following 10 categories：

1.According to the structure: 

fixed capacitors, variable capacitors and fine-tuning capacitors.

2.According to electrolyte : 

organic dielectric capacitors, inorganic dielectric capacitors, electrolytic capacitors, electrothermal capacitors and air dielectric capacitors.

3.According to use:

 high-frequency bypass capacitors, low-frequency bypass capacitors, filter capacitors, tuning capacitors, high-frequency coupling capacitors, low-frequency coupling capacitors and small capacitors.

4.According to the different manufacturing materials: 

ceramic dielectric capacitors, polyester capacitors, electrolytic capacitors, tantalum capacitors, advanced polypropylene capacitors and so on.

5. High frequency bypass: 

ceramic capacitors, mica capacitors, glass film capacitors, polyester capacitors, glazed glass capacitors.

6. Low-frequency bypass: 

paper dielectric capacitors, ceramic capacitors, aluminium electrolytic capacitors, polyester capacitors.

7. Filtering: 

aluminium electrolytic capacitors, paper dielectric capacitors, composite paper dielectric capacitors, wet tantalum capacitors.

8. Tuning: 

ceramic capacitors, mica capacitors, glass film capacitors, polystyrene capacitors.

9. Low coupling:

 paper dielectric capacitor, ceramic capacitor, aluminium electrolytic capacitor, polyester capacitor, solid tantalum capacitor.

10. Small capacitors: 

metallized paper dielectric capacitors, ceramic capacitors, aluminum electrolytic capacitors, polystyrene capacitors, solid tantalum capacitors, glazed glass capacitors, metallized polyester capacitors, polypropylene capacitors, mica capacitors.

Function of Capacitors：

1. Coupling: 

The capacitor used in the coupling circuit is called coupling capacitor. It is widely used in resistance-capacitance coupled amplifier and other capacitance coupled circuits to isolate DC and AC.

2. Filtering: 

The capacitor used in the filter circuit is called filter capacitor, which is used in power filter and various filter circuits. The filter capacitor removes the signal in a certain frequency band from the total signal.

3. Decoupling: 

The capacitor used in the decoupling circuit is called decoupling capacitor. This capacitor circuit is used in the DC voltage supply circuit of the multistage amplifier. The decoupling capacitor eliminates the harmful low frequency cross-linking between each stage of the amplifier.

4. High Frequency Vibration Elimination: 

The capacitance used in high frequency circuit is called high frequency capacitance. In the audio negative feedback amplifier, in order to eliminate the high frequency self-excitation that may occur in the amplifier, this capacitance circuit is used to eliminate the high frequency whistle that may occur in the amplifier.

5. Resonance: 

The capacitor used in LC resonant circuit is called resonant capacitor, which is needed in parallel and series LC resonant circuit.