Cognizance 
Cognizance is not defined specifically anywhere in the code of criminal procedure,1973.It means merely becoming aware of an offence by a magistrate with a view to proceed with initiation if proceeding.It is a central stone of trial.Cognizance of offence is taken by magistrate u/s 190 of the code.Cognizance is taken by:-
1)Any magistrate of first class.
2)Any magistrate of second class empowered by chief judicial magistrate.
As defined in section 190(1), magistrate may take cognizance of any offence:-
1)upon receiving a complaint of facts which constitutes an offence.
2)upon police report of such case
3)upon information received from a person or upon his own knowledge.
Magistrate can take cognizance of protest petition also u/s 190(1)(a) treating it as a complaint.Power of taking cognizance of an offence is a discretionary one.He acts in his own discretion,not bound by opinion if anyone.The supreme Court in case of Abhinandan jha&others v Dinesh mishra 1968 AIR 117,1967 SCR (3) 668,held that magistrate is not bound by the opinion of anyone while taking cognizance of an offence.
Magistrate shall not refuse illegally to take cognizance of an offence.The word 'may' in section 190(1) of the code will mean must in a situation where material placed before the magistrate perversely or on some extraneous considerations refuse cognizance.Such uncanalised discretion will be frowned upon by the constitution.It was held by Supreme Court in the case of Shri AC Agarwal vs Mst Ram Kali 1968 AIR,1 1968 SCR(1)205,that where material is sufficient enough for any judicial authority to come to the conclusion of taking cognizance and if magistrate refuses to take cognizance,then the word 'may' in section 190(1) should be read as 'must take cognizance'.
Section 191 deals with transfer on the application of accused.It states that when a magistrate takes cognizance upon his own knowledge,then accused can change judicial magistrate according to his desire before taking any evidence.It is based on principle that:-
1)No man can once be a judge and a suitor.
2)No man can be a judge in his own cause.
Any irregularity regarding this provision cannot be cured u/s 465 of the code as a result of which trial will vitiated.
Section 192 deals with making over cases to a magistrate.
Section 193 deals with cognizance of an offence by a court of session.
Section 195 provides a bar to take cognizance of prosecution for contempt of lawful authority of public servants.
Section 196 provides bar to take cognizance of an offence against state and for criminal conspiracy.
Section 197 deals with taking cognizance of an offence relating to prosecution of judges and public servants.
Section 198 deals with taking cognizance of an offence punishable under chapter 20 of INDIAN PENAL CODE(RELATING TO MARRIAGE)
Section 199 deals with taking cognizance of an offence relating to defamation.