This article contains a presentation of all the main amendments to the Penal Code introduced by the Act of February 20, 2015 amending the Act on Penal Code and certain other acts of law (Journal of Laws of 2015, item 396). Most of the provisions of this Act entered into force on July 1, 2015. The change of the criminal law carried out by this Act provides the most extensive amendments to the Penal Code of 1997 from the time of its adoption. The reform of the criminal law was decided due to the defectiveness of practice. At the stage of preparatory works, an emphasis was put on the abuse of custodial sentences with a conditional suspension of their execution, a low rate of individual fines and a too infrequent use of fines and penalties of restriction of liberty. Also, a defective practice was underlined referring to determining the length of a penalty period involving deprivation of liberty at an excessive level in the case of applying conditional suspension of its execution (when the courts determined the term of imprisonment sentences at the level which is much higher than if this sentence was awarded without a conditional suspension of its execution). An emphasis was also put on the presence of high levels of prison population, a high percentage of those serving prison sentences and the existence of a large group of approx. 70 000 people waiting to undergo imprisonment. Most of the changes introduced by this Act refer to penalties. The main changes include creating a broader possibility of applying non-custodial measures. Also, a novelty is an introduction of the possibility of combining the penalty of restriction of liberty with the penalty of imprisonment (which is often referred to as a so-called “mixed punishment”). A number of changes concerning the rules of application of probation measures was introduced. When it comes to conditional suspension of punishment, the possibility of conditional suspension of the penalty of restriction of liberty or an independent fine was excluded; moreover, the possibility of applying this institution was limited – as a rule – only to custodial sentences with a maximum term of imprisonment of one year. In the summary description of the changes to the Penal Code in the article it was emphasized that the far-reaching changes which were introduced were justified mainly by ad-hoc practical considerations. It was considered that the amendments to the Penal Code follow the erroneous – from the point of view of rationality – trend of attempting to solve the current problems of practice by introducing substantive changes. The article also presents subsequent changes to the Penal Code resulting from two acts enacted on the day of March 11, 2016 (Journal of Laws of 2016, item 428) and Journal of Laws of 2016, item 437). The changes referring to the regulations amended or introduced by the act which was discussed in the article were indicated. These changes consist, e.g. in eliminating the new form of execution of the penalty of restriction of liberty associated with the use of an electronic surveillance system and in repealing Article 59a giving rise to the discontinuation of criminal proceedings against the perpetrator, who, prior to the start of the trial in the first instance, repaired the damage or compensated the harm caused, as well as in repealing Article 60a on the so-called “plea-bargaining”.